TV and the entertainment industry as a whole is incredibly competitive. Women have a limited shelf life and are disposable in the entertainment industry, (arguably more limited and disposable than men) and are judged more by their looks than talent. Alesha is 33, she must realise that in industry terms she is already past her prime shelf life, and on a slope downwards. Just for the record, I don't like, accept or agree with these sentiments, but that is the way it is.
I think new people are coming in on Strictly, so not only does she risk stagnating in terms of her career, she risks being rather un-illustriously booted when new producers, et al, want to make their mark on the new series and shake things up, which they are highly likely to do. For all we know, she may have already been given indications of this, hence her move.
In terms of making money and holding on to some sort of career, I think it was quite a smart move, she risked stagnating at the BBC she tried to relaunch her music career there with mediocre success. BGT is not the best program to move to, but don't be surprised to see her move to Xfactory if all goes well with BGT. I think she realised as well, that if she moved to Xfactory last summer, she risked the same sort of backlash as she got when she first joined Strictly, because of the whole Cheryl Cole melodrama.
And this loyalty thing to the BBC? Are you kidding me? Do you remember Arlene and the way the BBC treated her? C'mon now. There is no loyalty in the entertainment industry, and the BBC wouldn't think twice of kicking Alesha off the panel for whatever reason if they wanted to. The entertainment industry is a nasty, competitive business. If the 'average' person was offered a better paying job, with potentially better prospects, potentially better future prospects, better connections and better job perks, most people would take it.
Saying all this though, I do think last series was her best series, and she seemed more comfortable. I also think it's a rather sh*tty program she is moving to, but then, it's a career move and a foot in the door within a company that is in an area she wants her future career to be in. It's a risky, but wise move.