Of course, that is a system-level change, which can potentially break other applications on your machine (if they're written badly and/or poorly supported). .NET Core removes that by supporting side-by-side versions and versions packaged with the app, but it certainly wasn't critical to assume a given machine already had a .NET Framework version in question.

Honestly, with Windows 10 now including .NET Framework updates along with feature upgrades every six months, and the fact that pre-Windows 10 versions of Windows haven't that many more years to live, it feels like that advantage isn't as big as it used to be anyways.

My concern is .NET Core may lead to a lot of unnecessary software bloat. Where Windows has the current .NET Framework, but we still have to have six versions of .NET Core installed, and then half the programs on the computer don't use those and have their own bundled versions as well. I find .NET Framework already being on-system to be a big perk of writing my app with it: My software is a 7 MB file because most of the code is already built into Windows.