It's like buying a ticket for a concert, realizing you can't go and that you can resell it for more than what you paid.

You're right that long term it should stabilize into a low margin business.

Elon is also much less risk averse than others, which helps to build stuff fast, possibly cheaper, pushing legality to the limit. Colossus was definitely built much faster than anything else. I think building datacenters suits him better than a pure software play, where "move fast break things" is already the norm.