If steam changed all the "Buy" to "Rent" on it's website, nothing would actually change.
I'm familiar with Rent and I intuit what it means. I have access to an asset for a limited time, and then I can choose to continue renting it, or not. The decision is in my hands.
License might be a better word. Because what they're selling is a "one time payment for use of this asset for an undetermined amount of time" - that's not "buy" but it's also not "rent".
When my license ends it's likely I can't get another. Certainly its not my decision to make.
The period of the license us unknown - till you block my account, till you go under, till you decide this service is no longer available, till _your_ license-to-license expires, and so on.
So yeah, I don't think it's Rent.
That is not implied by the term rent. Very often rentals are for a fixed amount of time. Especially for video game rentals, back when they were common.
I think rent implies you have limited control better than license does.
Ex. if access is revokable, it's illegal to use the word "Buy" alone - have to use "Rent" or "License" or "Buy License" or something that doesn't imply ownership (because ownership is not being offered)