Yes it is rare, but it does not take away that this is part of the game currently.
Magic & Mayhem was part of a seasonal update and thus was getting removed when the season 'finished'. Gamemodes designed for a shorter amount of time, just as Magic & Mayhem and Ender/Carving Chaos right now, are being removed after 1/2 months (some will return, some won't).
However they are part of an update and make certain seasons more special. Let's be fair, the summer event wouldn't be as special/fun as how it was right now without Magic & Mayhem. In my opinion those gamemodes are 100% worth the time and resources because of the hype around them.
On the other hand we have TNT run, suggested in this thread, I believe that putting the time and resources into developing, designing, testing, etc of this gamemodes are not worth it when there is a huge chance that the gamemode would not get enough attention and because of that will get removed after a Beta period. This effort can be used in many other projects with way more priority.
That is possible, for sure. But how big is the chance for TNT run becoming incredible popular on Bedrock while it is one of the gamemodes on Java with the least amount of players.
So your opinion about staff being 'not good' is based on when someone disagrees with your suggestion and gives their thoughts about it?