For Edge, it's probably at least partially because Microsoft doesn't want you to end up in a situation where you have no browsers on your computer. You can't expect the average user to not be stupid enough to uninstall Edge without having another browser installed, nor can you expect them to figure out how to install a browser without one.
The same goes for things like an image viewer or video player; you can install alternatives, but Microsoft doesn't want you to end up in a situation where you lose core functionality on your computer. They have no guarantees that whatever alternative you install has the same capabilities as what's bundled by default.
For Edge, it's probably at least partially because Microsoft doesn't want you to end up in a situation where you have no browsers on your computer. You can't expect the average user to not be stupid enough to uninstall Edge without having another browser installed, nor can you expect them to figure out how to install a browser without one.
The same goes for things like an image viewer or video player; you can install alternatives, but Microsoft doesn't want you to end up in a situation where you lose core functionality on your computer. They have no guarantees that whatever alternative you install has the same capabilities as what's bundled by default.