I think the main reason why Elon Musk is so interested is because he is one of the big whales that is hodling a very enormous amount of dogecoin in his wallet.
That's just the reason for several other reasons from Elon Musk, because Elon Musk's goal of choosing Dogecoin is only to gain profits through price manipulation that he deliberately makes together with his fellow investors.
Already saw his new post on his Twitter yesterday promoting the DOGE coin again, and from what is I am seeing now it doesn't have an effect on doge coins price right now, I'm sure people now are aware of his manipulations in the crypto market.