This is wrong. Yes, they require constant maintenance. But that maintenance is pretty limited in scope, if it is required even. All they have to do is to push some updates once or twice a year at max, and maybe update the usage of some APIs. It's not like these companies can't do it. In the grand scheme they wouldn't even notice it if one of their developers would do that.

It's that they just don't want to. They're greedy as hell, and they don't care about you.

Even if it would be too much work at one point, e.g. if Apple would finally update their Bluetooth stack more often then every 10 years, and the API completely changes. Why not just open source the whole app, or at least their interface so independent developers could develop something so not all of their products need to go into the waste? Because even in this hypothetical scenario, one thing holds true: They're greedy and they don't care about you.