The issue IMO, is it's not obvious that the battery needs to be replaced and when. It's not holding charge > new battery is far more obvious than it's slow > new battery. Most people probably prefer a slow phone than one without charge however Apple should have some indication of what's going on.
They wouldn't even LET ME PAY FOR THE REPAIR.
Then you would know that it is totally their fault and the liability would be on Apple to fix other people's devices.
My phone randomly shuts down or rapidly loses battery once it is below 40%. It's even worse when it's cold.
Or you know, Apple could make it easy for the user to replace the battery by themselves. But they chose not to.
This is the engineering equivalent of saying, "Why doesn't someone just go to the Middle East, sit down at a round table with with the Israelis and Palestinians and Sunnis and Shiites and rebels and Baathists and Saudis and ISIS members and refugees and all those other guys, and help them work out their differences peacefully?"
And yet, they didn't. The world didn't need yet another security screw.
If the market wanted such a thing, then guess what... the market would get it.