That is the weird part about it, he is not really a great investor himself, so it would be weird to listen to him when investing into something. People look at the companies he bought or founded and think that he is a great investor, but the reality is that when he "invests" it is not that great, only great when he manages a company and there is a big difference between having 5% of a company and profit from it, or own 30% and rule it with iron fist.
I think Elon is also a very very weird dude, he says it himself and that's why it's not reasonable to expect him to invest into reasonable stuff neither, he would invest into wildest things ever because that's what he likes to do.
This is in fact a good point, if you take a look at some of the richest persons alive you will see that they either hold huge political influence like a president or possibly a king or they are people that built their companies almost from zero like Elon, seldom you will find at the very top an investor, the most known exception of this is Buffett, as such when it comes to investing Elon is probably not the first person that comes to mind, especially since his most recent investment which is Twitter is not doing well despite his best efforts.