Well I know that personally, I tried to get to any EM events that got held. Sadly since I work second shift, or I have plans, I almost always miss out.
I try to go to player events as well, but the same thing happens. It's rough for people who only play past midnight with any regularity. But I digress.
I think QZ is right about the iffy appeal of em events. Most people show up for whatever uber kewls the robe may be dropping on stuff, hell, I won't deny it, thats why I go. I am a pixel junkie, but its a big turn off to some people to deal with all the greed that happens.
Also the events themselves are generally pretty lame honestly. Im not even saying thats the EM fault. I really don't know, but a lot of the time, its some random thing like "Everyone rally at xxx location, xxx is there being evil! Kill it!". I really just don't think EM have the powers/time to make a compelling story happen.
On the other hand, player events are easy for everyone. If its just some players wanting to meet up and chat... no pressure, no expectation. Just a good time with friends. Why not go?
I do think that there is also an issue with events getting raided, and the pvmers needed to complete the event getting killed. Now, I'm not suggesting that this is wrong persay, I think the real problem is that there are VERY few of the old cut of pvper, those who played to PROTECT those who needed it. To defend from raids, and protect the noobs and pvmers.
Back at Wispwood in the hey day there were some pretty bad ass shirefolk who would keep the baddies at bay while the rest of us cowered in the tavern. Thats how it should be, but those peeps are gone now. Perhaps the game is just different.
Really I think all an EM for siege needs to do do be popular and helpful, is two things:
Firstly once a month have a night that starts with a meetup maybe at a specific location, for a hang out, meet and greet (new people are always puzzling over where to find people, this would help) maybe with some simple games, like mongbat dartboard, archery competition, costume competition, chicken battles, etc with appropriate door prizes, then after gate everyone over to an arena for a pvp tournament. Make it like a monthly festival, which lasts a better part of the day. Plenty of food, fun, and fights for all.
Secondly: Occasionally drop a hoard of buffed up purple balrons (or cows or snakes, whatever) on luna, or umbra, or the new attempt at a player village. Have the drop magical orange ferns...whatever, just some fun monster killing to do with some stupid trinket to remember it by. Nothing stressful, no story or boss even need.
Those two things are both pretty uninvolved, and I think people would be into them.