he didnt invent bitcoin to be a hoarder/rich
he was a programmer trying to debug.
he obviously changed addresses for that purpose and also every time he done updates and changed wallets the addresses would change

its pretty much common sense back when bitcoin was worthless he didnt care much for wanting to keep funds to spend. (no value)
also he had the mindset that the more coins that are lost the more potential value the other coins other people would have due to less than 21m supply remaining, due to less than 21m access

as for potential questions i feel this is going to lead into being asked:
along with bugs and other issues when doing updates, its basically common knowledge that he probably doesnt have them keys anymore, so no big chance of a sudden spending spree in the future