It has been a while Elon Musk shill for DOGE and that's what happened today again. 2 tweets from Elon Musk. Both were interesting. But I don't get the exact reason of his shilling behind the shilling. He once said he only owns 0.25 BTC which his friend gifted him long ago.
He is doing it because he likes too. Freedom of information 
He is doing it on social media where anybody can say anything anytime they want and many people can see it.
Besides, he is probably joking about his tweets because after all DOGE is just a meme/joke coin and will always be like that. He can shill anything that he wants. It will depend on his supporters if they will react to it or not. Since he started shilling it, I didn't tried to buy it not because I'm too late for it but its just that I don't really want to involve into it.