You have a perpetual right to use the product you bought. You don’t have a right to upgrades in perpetuity.
Your point is valid as well. There's no reason both of our preferences shouldn't be accommodated.
Sketch (the prototyping app) did the right thing and offered both. One-time fee for lifetime use with 1 year of upgrades, with an annual payment option for continuous updates. I bought a license in 2019, have never needed to upgrade.