He just realized that he can, so he does it.
Probably got on the market before the BTC/Tesla announcement and then pumped it, then thew DOGE in the for the memes and then Tesla announces that BTC consumes too much energy and that are looking out for a greener alternative. ETH is switching to PoS. At this point, he is probably slowly filling bags of ETH and gonna pump as soon as PoW on ETH ends. Expect a series of excited twits from Elon then