Maybe elon bought dogecoin before the time that the price of doge is very low and now he is making money by the power of his influence , by just simply tweeting doge and after he tweeted now his ready to slowly selling some of his doge and he repeat the process until his all doge totally discarded.
That could be the case but some people said elon only owns small amount of the coin but to be honest none of us in crypto space really honest about the existence of our asset to not get unnecessary attention.
There's reason why elon keep tweeting again and again and maybe that have to do with him growing his asset but that's just my wild hunch, don't take it seriously, moreover tesla company already invested to btc so it's kinda possible.