Multiplayer likely accounts for less than 1% of the Mount & Blade franchise, the notion that the extra multiplayer feature was ever an attractive factor for people considering purchasing the games is a completely nonsensical notion. It's a niche community within a niche community.
In the Bannerlord multiplayer beta, there has been thousands of beta invites sent out, and by my estimation there's less than 200 unique users who have spent more than a couple of hours playing, I always play against the same people, and you can check out other people on the forums who claim the same thing. This should be an indication of just how low the interest for multiplayer for this game is.
Taleworlds should, if they know their own playerbase, focus almost entirely on the single player and modding capabilities. Multiplayer always was and should remain a secondary afterthought.