Well I can't say this applies to me, since I jumped to Pathfinder, but my previous table of friends did stick with 3x, and I know why. The majority of those friends are unemployed (or were, some have jobs now), but over the past almost 10 years. One of them purchased nearly 100 Wotc and 3PP 3x hard bound books, and now she is unemployed. When I jumped to Pathfinder, I did my best to convert them to PF. With the huge investment in 3x books, and the fact we mostly played games at the house of the woman who made all those purchases - she
wore the pants at that table, and insisted "if you want to play at my house, you're playing 3x, not PF". While I stuck around for another year playing with them, when my trilogy of modules for my published Kaidan setting of Japanese horror (PFRPG) was finally released (in 2010), they refused to give it a try (because it was for Pathfinder). So we parted ways. I think in their situation, I understand - and that's the reason they stuck with it.
I don't, but if I did want to run a d20 game, I'd go with 3.5, just because I have a lot material for it, whereas I only have the core book for PF.
Honestly, I've only purchased the Core, APG, and Paizo gave me the GMG (to help me in writing the City of Kasai Gazetteer for The Empty Throne module, Jade Regent AP). I rely on
d20pfsrd.com instead of having a need to purchase anything. There's no need to purchase to play PF, is all I'm sayin'.