That's true, but in my opinion unless there's actually some active on-going service, just charge for new versions and/or maintenance. This whole saturation of everyone charging everyone $10/month is tiring and frustratingly expensive as they know most will not pause or meter their billing in periods of inactivity.

There's still examples of software developers charging for software. For example, https://www.just-great-software.com only sells their software, they don't even charge for new versions or updates most of the time nowadays.

Yes it may not make a fortune, but with some ad-buying maintenance, upgrades, etc. there's likely an okay business.