Why do some developers charge 3x for the same app across iOS, iPadOS and macOS? Do you not feel embarrassed?

Why are there apps that charge, for example, $10 on iPhone, another $10 on iPad, and another $10 on Mac, despite the fact that the iOS version already runs perfectly fine on iPadOS and can often run on macOS as well, sometimes with only minor limitations?

I understand that a proper Mac app can require additional development work. If you're actually maintaining three substantially different codebases, providing a completely different UI, adding Mac-specific functionality, etc., then sure, charge accordingly. But most of the times we're talking about the same App with just small improvements. The developer didn't suddenly have to develop the app three times. In many cases, Apple literally provides the frameworks and mechanisms to make the same app available across iPhone, iPad and Mac.

Also, in most of the cases I tried (with PlayCover), both, iOS and iPadOS Apps run just fine on MacOS. So why again disable to download them natively on macOS? Greed?

And before someone says "just don't buy it": obviously. That's not really the point. Especially when Apple's own ecosystem is built around the idea that your devices work together seamlessly, that's just sad behavior.