I don't believe that servers such as Era or Zodiac are the cause of the decline in guild activity, nor do I think that they actually contribute that much in the downfall. As these servers have arguably more gameplay than the others, people are obviously going to play them and leave their home servers. If guilds were fixed on a global level it would provide a backbone for servers to appropriately cater for them, and it is up to the servers to provide the gameplay for guilds. Classic hasn't got much gameplay, and they're trying to work on that, but because of the problems facing guilds on a global level it is very hard to offer content for guilds specifically. The problems are evident in the recent thread
Guilds and Warring, where it was proposed to use a local guilds system in order to avoid them. It's the use of local guild systems on servers like Classic and Unholy Nation that are taking away the purpose of the global guilds, but if support is provided on a global level it doesn't have to be like that.