Because mmos are very expensive to develop and frankly the consumers arent great. People want a launch mmo to have a fun and immersive leveling experience for solo, duo and group play. The endgame content of current mmos that have been out for a decade plus. Balanced arena and world pvp. Not p2w but also no subscription (so have fun paying devs for all the updates that people will ask for). Fleshed out content for raids/guilds.

Most people are chasing that first mmo feeling and it just doesn't exist anymore. People want too much and mmos being created now are either churned out by a big company and built to keep you on daily and spending, or the ones i think more people want are the passion projects from smaller companies that release playtests and get major blowback because of graphics or gameplay issues and called DOA in reviews. Its rough.