If I buy version 2 then it's mine and I can continue to use it for as long as I want, if I'm happy with the feature set. I can ignore version 3 or choose to buy it. If I buy it then I now own two products instead of one. Sometimes the older version might even be better (e.g. features I like have been removed or made worse).
With a subscription model I'm forced to pay again and again even if I'm perfectly happy with version 2.
Given "there was a time that subscriptions for software were virtually unheard of", it's safe to assume we're talking about more than a couple of years ago. To talk as if most users always used to upgrade, suggests you might be young enough not to remember the software industry before a decade or two ago.
In general, users very much didn't upgrade. That's exactly why the industry forced subscriptions on us. They weren't getting income anymore, when the older version of their software did the job perfectly well.
I wasn't an automatic everybody upgraded on day one like subscriptions are, but it amounted to similar: regular upgrades over time.
With subscription,the only thing certain is that the seller wants to do as little as possible to keep taking my money. This tends to result on product updates that benefit them.
There's a big difference between software you buy, run on your computer, and don't expect to be constantly updated, vs. an online service that you expect to stay up and serve you new content forever. In the latter case, if a customer drops off after 24 months, that lowers your costs. You can't reasonably charge a user for the number of months they could potentially remain subscribed.