It's for the same reason he's pretended to be a genius his entire career, he's obsessed with his self image and being number one. He's lied about being the best quake player in the world at some point. He's like Billy Mitchell with more money.

Fragile masculinity combined with wanting to appear sufficiently tech savvy to tech bro investors. Tech bros want nerds because pretty much every dollar they've ever made was off the back of some innovation of someone they consider a nerd, so Elon wants to be the biggest nerd to tech bros so they will throw even more money at his dumb projects.

Imagine being the wealthiest person on the planet, and still being this insecure.