i assume you meant to say "you can't chargeback..." since you're pointing out there are time limits.
in my experience the time limits are related to delivery of the service. for instance, you pay with credit card for a service happening 9 months in the future. if the appointed day arrives, and the service is not performed, there won't be a problem getting a charge back even though the actual charge was 9 months old.
i'd certainly make that argument to my credit card company if steam cut me off completely.
i don't think it's crazy for a software company to want to claim that i'm leasing software from them after a one-time payment, but if that's the case, i also feel like i forever have grounds for the return of my money if they ever break the lease.
in my experience the time limits are related to delivery of the service. for instance, you pay with credit card for a service happening 9 months in the future. if the appointed day arrives, and the service is not performed, there won't be a problem getting a charge back even though the actual charge was 9 months old.