Actually, you can interpret it the other way around. If it were a transitional team we were talking about, there would be more chances for players to break through, whereas if it's one of the best teams in history the chance is a lot slimmer. I guess every player has his own reasons, but at least, to cite a recent example, Nolito would probably have had many more chances at the wing if it had been the Barcelona of the late 90s or early 00s, with an inconsistent and injury prone Overmars, or later on, a supremely unreliable Quaresma (to recall high profile examples). By the same logic, Fabregas would have had more chances had he stuck through as Iniesta was no more than an emerging promise, Xavi was still being questioned by the media, and Riquelme was... well... long story - whether or not it had to do with him being misused, played out of position, or having trouble adapting, the point still stands. Cesc had more reasons to stay given the apparent opportunity, but he decided to jump an apparently sinking ship.
Now, Thiago has the daunting challenge of being the substitute of Xavi, now recognized for his unique ability and even called the best midfielder ever, and Iniesta, also rated very highly. Yet, whether out of confidence or loyalty, he has so far decided to stay. It has far more merit than Cesc's departure.
There are valid arguments both in favor and against the purchase of Cesc, but either way, Thiago's future in the team should have nothing to do with it.
Ain't gonna happen. 
