Software used to be an investment. At university, our physics department had a lot of old computers standing around, whose only purpose was to run some specific legacy software that was no longer maintained, but still worked perfectly.
During my time there, I convinced the theoretical physics department to buy a few Illustrator licenses so we could make better diagrams. I think the academic license cost 300€ per seat. They probably never updated, but I'd assume they still have a PC somewhere with one of those licenses installed, and if someone has a PDF from Inkscape with an incorrect Color Profile, they could still use that machine to fix it.
I think you underestimate how many people use old software out there. Sure, we tech folks update every year, but people who work outside of the tech bubble don't always upgrade a system that's working perfectly fine.
If you need more than just photoshop, the deal is even better.
Here’s the reality. I used to pirate Adobe software because there was no way I was going to pay 1500k or whatever Photoshop was. Adobe got $0 from me.
Now I subscribe to get access to Photoshop. Adobe now gets £100 from me a year. I’m not the only person I know who went through this.
Of course, cheaper alternatives always existed. Adobe’s adoptance of subscription pricing hasn’t changed that.