Apple's customers are the >1 billion user install base it has for iOS and more broadly the Apple ecosystem.
Developers will develop great desktop and mobile software because that's the way to reach the incredibly valuable install base where consumer spend is 2x+ that of competing platforms.
You don't win developers purely by giving them nice developer features. You win them by giving them something worth developing for. Part of that is a nice developer ecosystem, but that not enough on its own.
They don't care about those that use macOS as pretty Linux/BSD replacement.
Just like NeXT never did, UNIX compatibility was a means to bring UNIX software into the platform, that was all.
Of course it isn’t. And that tells you that it’s a deliberate decision not to, because it’s miles from the platform’s intended use by the intended users.
Besides, it would be very confusing for users to have a terminal that can only connect to remote systems (which most people likely don’t have access to), because it’s rather improbable that Apple would choose to expose iPadOS through a shell.
Furthermore, the terminal could be simply running in a little Unix sandbox, like Termux, and that could be a great entry point for kids to lots of different interpreters to learn programming. Not exclusive to remote into other systems.
Even as a learning experience, why give (power)users the ability to acquaint themselves with a generic platform that is not tied to Apple’s own offerings? It makes no commercial or even pedagogical sense.
Try out iSH: https://ish.app It sounds like it’s what you want. Apple won’t be providing anything even remotely comparable for the foreseeable future, I’m sure.
Also, is it that hard for a giant of Apple's size to put a fully fledged terminal in iPadOS?