Just price and marketing. Pricing, customer segments, and product quality determine if your customer wanna pay for your services as one-off or continuous supporting you. I don’t every think i will buy a single simple 3D asset (such as , maybe a door) with subscription, but I am okay to pay for smart asset or even programming framework (with continuous upgrade/ new features) with subscriptions, music loyalty to use in different scenario. Just depends.
Subscriptions sometime also give buyers an alternative to do something just one time / one project with a lower prices, hard to say it’s good for not, but fit or don’t fit the used case and requirements . 