I go more for technical factors:
1) There was a bunch of new Open PvP servers for South America recently. Remember that a good chunk of tibians are most likely to be brazilians nowadays. These servers were new and had the BattlEye on it since introduction, so it was a good deal to get there for a lot of people.
2) PvP servers (now called Open PvP) are where most of old accounts usually wanted to gather with friends in the past. Back in the day, Non-PvP were crowded and full of people invanding respaws and Hardcore PvP were absurdly violent places. Even desert servers (like Obsidia) or war servers (like Thoria) were fine under some circunstances if you know how to deal with low respawn speed and PK groups in your tail. I can talk about these two servers because I played on both of them back when they existed.
3) Most of Open PvP have ok economies to get a new character going, so prices aren't super inflactionated (Optional PvP situation) or simply barely existent (Zuna & Zunera). Of course, there are exceptions to it, but Open PvP economies are decent on most of the servers.
4) Retro PvP is somewhat good for some aspects, but frankly these servers would be a little bit better if they were 100% retro. This topic is a complex thing to explain but overall I don't see much appeal for the current Retro Open PvP (maybe in the future I will change my mind).
And last, even with dominant guilds kicking you from decent respawns periodically, getting to a Open PvP place is a server that allows to you to fight back and even revolt if you feel the need to do so without extreme stress and economic spenditure. Getting blocked by noob characters and getting an expensive death isn't really something that I want to happen nowadays, with an aging community that needs to work, take care of family, etc.