You're correct. It is about supply and demand, but the only reason most guilds are so stable is because most of them have gone completely inactive, and thanks to all these changes and fixes, a great many have gotten tired and simply stopped playing. The more changes are made, the fewer are left to play, which means lower demand and greater supply. Class is redismissed.
Many guilds have gone inactive in recent years, but this has always been this way. The strong survive, however, not just because of the "high levels" as some have referred to the EOC folks (I, as you can see, am far from EOC) but because of the new players we add to our ranks. Take my guild, for example. Some of the oldest players in the game are here, granted, but we have many here that are relatively new. My founders diligently not only research what gear is best for all levels, but they also do whatever is necessary to have tagged gear available for us all. I don't use guild gear, as I'm OCD about owning my own, but many do use it as they progress along.
Many guilds do come and go, some die as members move to other stronger guilds like mine with plenty of gear and "high level" players for those good hunting buffs. All these factors affect the economy. JUST LIKE REAL LIFE!
Part of the problem here is that we all wear the same gear as we progress through the game. Common items, quest rewards, rare drops, anything that isn't a LE or SE set, they're only good to break down for composing these days, so those oh so important coordinated buffs will do their job. Maybe if we tried to be a little more unique in what we wore, depended more on our wits and math to make us one hit rather than these new age buffs, more gear would be of value.... Ever considered that?