Which is a great reason for Firefox to
not do it. Firefox sets itself apart by being different from the other major browsers, with a focus on user control and privacy by default.
I can understand removing features by default, but they should not be removed entirely. If user.js is causing startup to take longer and nobody uses it, then come up with a different way to check for it (e.g. about:config setting). If it's causing runtime or maintenance issues, then it might be worth asking the community if it's worth keeping.
