Because, dude bought it for 4x what its worth, and that is causing him some financial trouble. What he "worths" could be a lot, but what he has? That’s not enough to sustain twitter if it goes down. That’s a big problem for him, so he tries to keep it alive.
I see that he is still running Twitter very well and things take time to sort things out, he just took over it and has a lot to clean up and rebuild.
He's smart enough to pay billions of dollars for it, I don't think he bought it on a whim. Look at what he's got, that means he's on the right track, otherwise he wouldn't have become the richest billionaire in the world.
He bought twitter just to endorse his product. this is a fact that has not been implemented yet because of the situation. as we know twitter is very different when compared it with forum, but if he want he can make this forum be on next twitter with have mobile application download on android and ios. We still wait for this (the forum mobile) same as twitter, If Elon bought the forum and can do that (forum with compatible mobile application) tomorrow, There is no harm to support him.
Creating mobile applications is not too difficult and does not need Elon's support. I believe the administrators have a good reason not to upgrade the forum after all these years, perhaps they want to keep all the things that Satoshi left us, a pure original like bitcoin. But the idea of a mobile version is interesting, I also find it inconvenient to use the forum by phone sometimes.
