With the way guilds level now, I doubt many people are disbanding guilds dedicated to 25-man raiding. I'm sure that most of them are switching to 10-man raiding. Each active, raiding guild is the *only* thing that controls whether it chooses to raid 10-man or 25-man. There is no inherent barrier stopping an active, already formed guild from switching from 10-man to 25-man right now--there is no in-game penalty for doing so. I personally would be willing to be the GM, and raid lead, if I had to be, for a 25-man raiding guild. However, I very much enjoy being in the 10-man guild I am in, and it would take a lot to get me to leave them willingly.
I don't think the problem is there are plenty of cats milling about but nobody to herd 24 of them into DS or FL. I think the real problem is that 10-man raid guilds, with their shorter rosters (even if they have multiple 10-man groups, I'd expect each raid group to be fairly consistent week-to-week), form closer communities than 25-man raid guilds do.