Adobe announced recently at its "Max" conference that Photoshop and other Adobe products would be moving to a subscription model.
I can understand websites which use a subscription model - you (the customer) are regularly using services which they (the supplier) need to constantly maintain. Or a service like dropbox, which maintains a set of file servers constantly connected to the internet so that your computer can use them at any time of day or night.
Downloadable software, on the other hand, has been written, tested, and finally made available via a shop, downloaded onto your computer, and is expected to work as written.
It's a bit like electricity - you can buy it in the mains or in a battery. But charging a subscription fee or software that should just work is like trying to charge a subscription fee for a battery.
On a side note - lots of great graphics have been created with GIMP!