New version every 2-3 years which required a purchase. It was a few hundred dollars every time you wanted to upgrade (people may not remember this, but PS was the "value" product when it launched; professional software was often low 4 figures).

There's tonnes of companies that have legacy 'pay upfront' models, that hit the wall as they'd saturated their markets, then their revenue stream dropped off and all of a sudden saw the wall of transitioning to web/mobile needing to happen and didn't have the funds to pull it off.

I'd almost completely forgotten about it until I was challenged by a prospect in a meeting monday 'is this one of these new lease software systems, I want to own it!" had to educate him on the way the world worked now...

Subscriptions bring in steady money that allows for better forecasting and resourcing.

Releasing a Very Big Paid Update every year or two years brings in an unknown lump sum of money with a tail end that might or might not be enough.