All good points listed above but I'll add one of the major concerns I've found in detail.
Ultimately focus of a guild shifts as seen mainly between transformations from 10 to 25 man raiding guilds as well as the start of new expansions. Guilds are built to cater to a specific type of player. Though some guilds allow variance the main focus's are pretty clear. Once you try to overhaul that mentality (for instance going from casual to hard core raiding) you find resistance because many long standing members remained because of the way the guilds focus was before. Another instance is non raiding members because of, lets say time differances or work schedules, can't make your raid times but love the people then it shifts hard core raiding and business becomes about the raiding and regular guild activity to include basic conversations begins to leave those individuals out in the cold.
That's just one example.
Another would be lack of either guild management, officers competance, or simply time keeps the guild from evolving past one particular aspect and you find that many of your members get just plain burnt out. After wiping on one boss over and over again time after time or fast high weekly involvement in raiding forces constantly having to farm to keep up with the ever growing raid requirements and repair bills the game because a job more so then it's intent. And who wants to pay to go to work everyday? We have real life jobs for that and soon you find members getting burnt out of the enjoyment they once had.
And last but not least:
GM's who find themselves constantly taking charge of situations rather then putting the right people in leadership roles and teaching them how to deal with situations from the past as well as future events. To many times, and I find myself even guilty of this, GM's just want to get something done and fix mistakes right on the spot. Instead of chatting with the perspective officers and insuring they understand what needs to happen and deals with it for you. Especailly when an officer themselves make a mistake. Teach them and let them deal with it instead even if it was your idea because ultimately if the guild sees your the only one competent enough to handle their situations then no matter how minor they'll always come to you, never to them unless they have no choice and soon you find yourself overwhelmed with what could have been avoidable drama's and dilemma's.
Obviously you don't want to delegate everything but task them with specific duties that they over see and let them take lead. Talk with them private if they are unsure about something and then let them present it to the individual or guild. A GM who never takes the spot light or solves situations will soon find the members wondering why they are following you instead of following that other officer which eventually leads to guild splits and breakoffs.
There are many more I'm sure I can point out but I'm sure your eyes are already bleeding from this long winded post haha.
As always you can find me on US Ysera Horde as the GM of Prevail.