To me, anything that needs a server cannot be "buy once", because that would imply that the server availability for forever is included in the purchase. Which

To me, anything that needs a server cannot be "buy once", because that would imply that the server availability for forever is included in the purchase. Which obviously is not and neither should it be. You do make a good point that all, even local only software has a "best before" date, but online software is different: it has a hard expiry date. It is also prone to gradual price hikes and enshitification.