Everything is a tradeoff with phones. There is a tradeoff between phone size, battery life, and processor power. One day is a natural sweet spot since people charge their phones at night. Sure, this will result in a less-than-one-day battery life over time But people might have been happy to replace their phone anyway for other reasons.

Supporting old platforms is not just cross compilation, or at least the cross compilation involved is highly non-trivial.

I would say that excessive cynicism is as bad a bias as naivety. Everything you describe is actually consistent with perfectly informed consumers and profit maximizing companies. You are just not looking for explanations along these lines.