The shard population is extremely low, it cannot be argued. It reached critical mass a year or so ago when numbers reached a point at which shard activity became too low for any realistic recovery. The PvPers moved to Atlantic because there were not enough people to fight, and many people coming here are put off by how quiet it is.
As you stated, the Devs have done next to nothing to try and help Siege, despite our pleas. This isn't simply a case of not putting in rules changes, they have demonstrated that they have absolutely no understanding of the shard and couldn't care less about it. They fail to see Siege as a different kind of product, just a regular shard which is too troublesome to maintain. They did not allow Siege to keep unique EM rewards when they were removed due to the usual whines and moans from the prodo lowlifes, they did not keep the NEW advertising books despite them being a big boost for the short time they were there, and worst of all they are not prepared to promote Siege. We had a real boost to the population a few months ago when the shard was promoted by Petra Fyde of Stratics, which shows what can happen if someone "official" speaks out about us. This is extremely short-sighted in my view, as Siege was often a place that those from normal shards came to at the end of their UO days, and they may have been able to appeal to some of the "classic shard" lovers with a bit of effort.
Unfortunately, the population itself has not helped. Too many people have had their own agendas in the past and not looked at the bigger picture, and attempts to promote Siege elsewhere have usually ended up as shouting matches between Siege/non-Siege people. And it must also be said that the UO population itself is undoubtedly on serious decline. One only has to look at the number of threads in UHall these days to see this, and I'm not sure any shard is doing well with the exception of Atlantic.
The current Siege population is small but still a very friendly and generally good-natured bunch. But, as stated above, it is too small to lift itself up by its own bootstraps. The boost we had a while back has subsided and many have vanished into the ether. We desperately need more guilds. I had great hopes that the recently-formed CD guild would replace TnT as the all-round PvM/PvP "chaotic neutral" guild, but they have seemingly disappeared.