Has any Medieval MMORPG Gamemode ever been at least semi-successful?

As it seems, that many projects have been ran and well developed for MMORPG type gamemodes, and in the end nothing comes of it. Why is this?
It seems quite odd that nearly ever project has been abandoned, or started like Crussaria HGN but closed down due to lack of players. Was the scope too big?
I would believe a MMORPG is generally what the community would want, it seems to be quite fitting since there are other successful Roleplaying gamemodes like SWRP that have had massive success.
Another reason may be because the gamemode itself was too well developed for the average server owner to recreate, therefore no other servers but the original developers existed.
Which is why SWRP took off and other well developed roleplay gamemodes did not.

I would like to hear your thoughts on this as it seems quite weird that nobody would want to see a roleplay gamemode. Why do you think Star Wars Roleplay was a success while other roleplay gamemodes were not (movie release? easy to develop?)
Thank you.

People don’t want to leave DarkRP. At first you need to code an actually GOOD MMORPG gamemode, then you need to make your own server with high amount of player slots, then you need to make some popular guys from YouTube to play on your server, and only then you can release your gamemode to the general public. Community will do everything else by itself. You will need these resources: developers (it will take ages to code a decent MMORPG by yourself), testers (you can get them from Facepunch for free), money to pay popular YouTube guys, money to host a good server (OVH Game VDS will be OK).

TL;DR: you will need lots of effort to do that, and if you are not really really lucky you will need lots of money to pay for devs and popular YouTubers playing on your server.