Let's Get Real - the DM's responsibility is balance

[Pex]

You already only roll when doing mundane things. Proficiency is not even required.

Ability checks should only be called when:

1. The outcome is in doubt
2. There are meaningful consequences for failure
3. It's interesting

Most of the time the characters should just be able to do things. No rolling for walking across the room.

But DMs have no such guidelines when such a thing applies. One DM's trivial is another DM's need to roll is another DM's need to roll but at a higher DC, so mundanes don't get do to things reliably or at all. Spellcasters cast a spell, they never have to roll or any applicable DC is distinctly defined.

No rolling to walk across the room, but do they have to roll to climb a tree? That has never had a universal answer, in 5E.