I tend to have conflicting views on Beyonce (love most of her music, not always crazy about her as a person, don't think she 'writes' nearly as much as she'd have us believe). Now with my personal views on Beyonce out of the way I want to just say that this "blame [any really popular female] for [semi-relevant female artist] not being successful" thing is just played. With Bey in particular, this topic has existed ever since Destiny's Child became popular and she gets blamed for a lot of r&b artists' failures. People have this idea in their heads that Beyonce (and/or her team) won't "let" others be great. I would think that Beyonce has been putting in too many work hours toward being great herself to even have time to concentrate on actively squashing someone else's career.
Here is the thing. It takes a very huge, well-oiled machine to make any person a huge star and even then, it isn't a 100% guarantee that you will become hugely successful. Very few people are fortunate enough to get this kind of machine behind them and fewer still are able to make it work for a very long time. Music history is littered with thousands of would-bes who never made it, for reasons that have nothing to do with the handful of people who did:
1. Not having The Team (or in some cases, any team at all). This factor is the main Great Divider between the Beyonces and the Ciaras of the world. Most artists end up with teams that are either incompetent, de-prioritize them in favor of other artists, or just don't have the clout to push a person very far. Other artists, especially those just starting out, don't have a team at all and have to do everything themselves. So they don't quite know how everything works, or they don't know who the gatekeepers are and thus don't know who they need to be trying to connect to in order to break through.
It's important to know that just because one team is right for one person, doesn't mean that team can be right for everybody. A Dream Team for a pop artist will not understand the nuances needed to launch a band in the rock world. Labels regularly de-prioritize several artists for one favorite (see: Capitol and how certain urban acts got slighted after they merged with Virgin and put all their efforts into Katy Perry). American Idol is notorious for picking one or two favorites each season to "pimp" and then treating other equally or more talented people like crap; the viewing audiences are heavily swayed by this type of manipulation (although many will swear up and down they are immune to this, they're lying, don't delude yourselves) and unfortunately, this bias prevents most Idol contestants from finding a good team with industry influence to put full money and effort behind them after the show is over. I could write entire posts solely on how much I hate this kind of nepotism and label politics, but it's important to remember that it's not Katy's fault that she was favored; she is merely a beneficiary of the label's priority system and the only thing she owes to any of us is to simply work hard and prove she is worth the extra attention. Those getting the short end of the stick will gain nothing from being bitter about this; they have to find a place that will favor them instead. And if it's meant to be, they eventually will. (Hello, Jennifer Hudson.)
2. Music that does not appeal to the masses. For the most part I'm really just saying "crappy songs" because goodness knows there are plenty of those, but the truth is that I've seen great music flop and really bad music soar to the top of the charts. In those cases it is all about factor #1 (the team/promotion). So when I'm talking about factor #2 I'm really speaking about people who either a) simply don't make mainstream music or b) make music that isn't bad enough to get attention and not good enough to stand out. Pure urban music, for example, has had very little crossover potential for the past several years, and it is unrealistic to expect an urban artist with no crossover singles to suddenly explode and have #1 songs and multi-platinum albums. This isn't the 90's anymore. Yet this seems to be exactly what some people expect, and then when it doesn't happen they start dragging artists for it instead of recognizing a niche for what it is.
Then you have the people who just aren't putting out interesting music. The music is acceptable, but blends in too well with everything else already being played, thus they get overlooked. Not everyone wants to take the Rebecca Black path to fame I'm sure, but I bet more people will remember the novelty of Friday five years from now than anything Kristinia DeBarge or Paula DeAnda sang. And not having music that is interesting or memorable enough leads me to point #3.
3. Simply not being as talented and/or interesting as fans would like to believe they are. This is the one people have the hardest time coming to terms with. I can especially understand why they may be salty about the talent issue, as there are a lot of people of dubious talent levels getting hits these days. But the fact is, we can't all be special. Some - well, most - singers just aren't as compelling as a few others, and all the talent in the world won't make a difference if the audience is bored to tears or can't even remember the melody to your song five minutes after they heard it on the radio. I'm sure these artists are very nice people once you get to know them, but "nice" and "personality" don't go hand in hand. Now if they had a good team, then the team could try to create an image for them so that this issue can be avoided - to use Katy as an example again, I actually don't find her to have a very engaging personality, but her label and management have done a fantastic job of crafting a distinct and interesting image for her and effectively selling it. But few get that kind of team. Some may get that kind of team and it still is not enough, or it is enough for just a little while before the shtick wears then. In all of these situations one simply has to accept the fact that a particular artist just doesn't have that elusive "it" factor.
Now if you want to get into a discussion of why the industry seems to pick a certain few 'chosens' to be extremely successful or why certain artists seem to struggle or fall off without warning, those are different discussions altogether. But don't blame the chosen ones for the ill fate of others. At the end of the day an artist is only responsible for his or her own fate.