Except if they decide they don't have any updates to release for a month you just paid them for a month of nothing.
The issue with a subscription for self-hosted or locally ran software is that you are obligated to pay an ongoing fee, without the provider being obligated to provide the service you're paying for. Their terms do not require them to adhere to any release schedule or anything showing that by paying a subscription you're getting X. It's basically a recurring donation in hopes the software you paid for gets an update.