both formats deal with burn out and difficulty with raider retention, but its a lot harder to keep a roster of 28-35 players happy, organized, and getting along with each other then it is a roster of 12-17 people. the staunch large format raiders from vanilla/bc/wolk are slowly quitting, either burning out for good or growing out of the game, and the new generation of players of the caliber to replace them are not interested in running 25s.
10s don't need any more loot then they get, if anything they should get even less loot then they currently do. with both formats dropping the same ilevel loot there is really nothing to incentivise 25 man raids, thunderforged doesn't even incentivise 25 because 10 man get thunderforged too, but giving 25 higher ilevel loot would kill 10s and force people to run 25s ( i'm ok with killing 10s, but most people are not. its ok to force me into 10s with logistical issues, but not ok to force you into 25s with gear issues? fairness? what is it?). if your progression is decent, baring really really atrocious rng (despite having killed will on normal and heroic many times i've never seen the dps plate legs off it, but my friend's 10 man raid has gotten them pretty much every week) you will eventually get your piece.
and is loot really why we raid? if your only driving force behind raiding is your ilevel epeen then you should probably reconsider your priorities. loot certainly isn't why i raid, i raid because i enjoy organizing and problem solving, i enjoy the epic experience of vanquishing evil with an epic band of heros. i can't get either expirence in a 10 man.