Subscription models only make sense for an app/service that have recurring costs.

In the case of Lemmy apps, the instances are the ones with recurring hosting costs, not the apps.

If an app doesn’t have recurring hosting costs, it only makes sense to have one up front payment and then maybe in app purchases to pay for new features going forward.

Subscription models for an app that’s not hosting anything is just the dev wanting a constant revenue stream, no matter how they try to word it.