Earlier quoted context omitted.
Because the amount of users who don't care or notice performance or memory usage issues is immensely greater than the amount who cares.
IMO that's a poor excuse, and leaves open a lot of room for competition. There's a lot of hubris in assuming their position as a market leader is unassailable.
They're killing it for a reason, and it just may be that the market they're targeting cares more about the app Just Working than about the RAM consumption.