On one hand, renting other people's computers forever is very expensive compared to owning them, and it's possible that storing sensitive data on other people's computers comes with security implications.

On the other hand, this way we make sure we don't hire anyone or develop any in-house expertise in maintaining systems that aren't rented forever, and as a bonus we can claim to investors that our theoretical capability to scale up "infinitely" is a logical prediction of our future market cap.