It makes sense to me as removing the choice between, "Do I buy one-off license or a subscription?" If you get the subscription, you get a free one-off license at date of purchase.

Your way also makes sense, but they both seem reasonable to me. And I don't really care much, in that I renew when I'm regularly using their product, as I want to support them. If I just had to open an old project for something, then I don't mind exactly which old version I'm using. (And if I somehow did, I could just put it in 30-day trial mode.)