But it's not like improving twitter would improve the world like nuclear fusion, better batteries or a cure for cancer would - there are plenty of better invest

But it's not like improving twitter would improve the world like nuclear fusion, better batteries or a cure for cancer would - there are plenty of better investments. It's hard to even establish metrics for what "improvement" or even "success" looks like in the case of twitter. From Musk's standpoint "improvement"/"success" means he makes money (or at least doesn't lose a lot of money) on the deal. There are plenty of alternatives to twitter out there already and probably others being worked on. Twitter could disappear tomorrow and the world wouldn't be negatively impacted at all, in fact it would probably be a benefit.