Lol okay. Have fun with your assumptions that the service has value to everyone since that's pretty trivially shown false. Especially if they ever do change editions, WotC historicially has never let the tools or forums for a previous edition stand, even when paid.
But they aren't marketing it to everyone. They are offering three distinct options:
Option 1: Digital only, for those, like me, who just want it on DDB.
Option 2: Digital+Physical bundle, for those who, like OP want both.
Option 3: Physical only, for those who just want that.
Each of these is a distinct value proposition. I will make the case any day of the week that Option 1 offers enormous value for me, and given the rampant success of DDB, it apears that plenty of folks feel similarly.
I think it's been pretty clearly established that Option 3 offers competitive value, both in terms of the historical cost of official D&D books, adjusted for inflation, and in comparison to similar competitors, so it seems to be around what the market will sustain.
Option 2 is the one in question, and the OP has made it clear that, for them, it has crossed a rubicon where the cost is now greater than the value. I don't have a dog in that fight, so I am interested to see if they are correct. Given the way things have gone lately in terms of inflation, an increase from (typically) $10 to $15 for the addition of the digital rights doesn't seem egregious to me, but if enough folks agree with OP, WotC will have some hard decisions to make.
As for your worries about DDB essentially going away, I don't share them. I don't think they are likely to come true any time soon, and the value and convenience offered by the service FAR outweighs the risk, for me. I feel this way about susbscription services in general: they are extremely convenient, they save me a small fortune every year, they save me heaps of storage, and they produce far less waste. I think the world would be a much better place if humans stopped gathering so much stuff (as long as my miniatures collection isn't included, because I'm also a hypocrite).