FWIW the Pixel 8, the newest device offering Advanced Memory Protection, sells for less than $600 brand new right now. You can tune memory tagging & hardened memory allocation on a per-app basis. It's a game changer
You are saying that as if it was cheap. I am pretty sure most people buy <$250 smartphones. That is at least the case in my social circle, very few iphones, pixel, an awful lot of cheap Xiaomi Redmi and the Samsung Galaxies are usually the A line instead of the S line.
It's due to hardware reasons just as an FYI - I forget the specifics, so forgive me if this is dated, but I believe it had to do with some crypto-specific chip if I remember right.