Online subscriptions have actually been a thing for a long time. In some ways it's even fallen out of favor, especially with the rise of the "freemium" model. MMOs are a great example of this as subscriptions used to be the price of entry with no other monetization, where as these days if an MMO uses subscriptions it's a secondary "convenience" fee after entry that is almost always combined with MTX bullshit.

If you're talking specifically about SaaS bullshit, it's because it required a certain level of infrastructure before it became practical. We had to move away from cash and needed reliable internet connections first, amongst a host of other developments. Anything that couldn't be a cash purchase in a physical store was losing significant market share. This didn't stop time restricted licenses on software still being a thing, but it was generally pretty niche software.