Honestly, I get your point of view. It is valid for the isolated upgrade perspective. But of course the business model is a bit different. You pay to continue to use Platinum components together with updated core components - or keep the state of platinum.
I like the Cakewalk Software very much. Last year I started with Artist, that would have been enough for a long time. But then came the lifetime offer, and this was obviously a no brainer for me to update to Platinum.
So - it is your choice if you pay or not. Maybe it is worth to consider if the Pro or Artist variant might be enough.