They may well not be using the 'most current' version of the software, and I can think of a few pieces of software where that's been the case for me too. Either because I don't use it enough to justify the upgrade, or I actively object to being fleeced again for essentially the same product that's been "updated".
But eventually, if they want to continue doing the task they'll end up paying for a new version. Unless it's open source, it's always under the control of the product creator, and their incentives are always going to be on extracting money, and indeed they need to, to continue supporting the software.
In the Apple Ecosystem, the move to M1 Macs is an example that will force people to pay for upgrades.
Buying it once and riding it as long as possible is undoubtly cheaper than subscriptions, however it's still got a lifespan that eventually requires the next payment.