This is probably true. It's no coincidence that the largest, longest-running, and most legitimate tournament series for BL has been run by veterans of Warband tournaments, and tournaments which haven't been run by such people have fallen apart, were one-offs, or are finally getting through their growing pains only to find that there aren't enough people or teams to fill a bracket. This is not entirely the fault of these hosts, and Warband had similar situations. However, the environment provided by TW was different at the time.
Warband's competitive scene had ups and downs with patches during its nascency, but the time table for updates & receptiveness to feedback meant that no problem remained an obstacle for terribly long. The playerbase steadily grew during early access, and continued to do so until a while after release just as you'd expect from a healthy game.
Bannerlord has not fared so well, and the initial surge of players is all but gone. The new players who want to learn how to host events & run tournaments haven't had the benefit of a stable or growing population to participate or provide feedback. The glacial pace of updates has made all mechanical & balance issues long-standing ones, and delayed the release of features critical for competitive play (duel mode, premade team vs team lobbies, custom servers & game modes). Those that do host get discouraged after lackluster engagement, or are wrapped up in damaging drama that only perpetuates because there are no alternatives.
There is little incentive for hosts of events of any kind to continue putting effort into this title, and the likelihood of new blood picking up the reins is low because there is nearly no new blood. Even if they did, their potential scale is severely limited, and it follows that the subset of participants who would provide the feedback that drives innovation in tournaments is also reduced.
To say the approach to MP "hasn't worked" is like saying a race horse that trips out of the gate & breaks its neck "did not finish." Technically correct, but it doesn't paint quite the same picture.