Recruitment hurt my guild for a while in Cata, we lost members and couldn't replace them but we still managed to find enough to keep raiding throughout the entire expac. Then in Mists, it finally started to actually halt progression. We had our first tier halting due to recruitment in ToT - we couldn't ignore it this time. Our guild came back in WoD, emphasizing it would try to be less hard-core to bring in a wider array of players and try to build them up. WoD ended up experiencing the largest player drought it had ever experienced - we weren't losing just a one or two people in Cata here, or two to five people in Mists there, now we were losing upwards of 80% of the entire guild in WoD, and replacements came in slower than ever before across the entire game and it seemed like everyone else was experiencing similar drops across the community. The guild tried again in Legion, doing a merger this time hoping that the resulting merger would stem the flow of lost recruitment long enough to keep the guild raiding throughout the expansion again. This lasted maybe up to and through Nighthold, and recruitment again became an issue - we again were losing people faster than we could train them. For BFA the guild jumped factions trying to find better recruitment opportunities, but I haven't heard from them since.
This was a good guild, filled with good people, just trying to raid progression. The leadership was fair and good, the people were kind and supportive. I have nothing but respect for the people I raided with in this guild, but every expansion since I joined recruitment at the high-end was a problem. From expansion to expansion. While some expansions were so much worse than others as with WoD, and while others like Cata were easier than any other, I would be lying if I said I didn't notice a trend -- high-end competitive raiding just seemed to not have any recruiting power after Wrath. There just didn't seem to be enough people to go around to all the guilds ever since. It felt like in Wrath there were so many people you had to keep them back with cattle-prods and you were always overflowing with enough people to bring in to raiding teams. I can't say definitively what caused this entire recruitment problem to happen and persist since Cataclysm, but man has it been noticeable since Wrath. I've no doubt people have experienced their share of recruitment woes in Vanilla and TBC as well, but it felt like you at least had a chance back then. Nowadays recruitment feels more hopeless.