I mean I can make this up, but I shouldn't have to. Why not just write the bloody thing in the book? They already wrote that you can increase the distance by a check, give the actual numbers too! And having them in writing helps with being consistent. Will you remember the next time that exceeding the jump distance by six feet was a DC 20 check?
You don't grasp the problem. Since it is the DM who decides the exact wideness of the chasm, probably by looking into a list how far it needs to be for a certain check, why go thorough all those hoops and just decide for a check and tell the players that the chasm is a bit too wide to easily jump across.
If one player tells me his character is exceptional at jumping, why should I tell them ah, i see, you can jump exactly 19 ft. But too sad, my chasm is exactly 20 ft across. So your extraordinary ability is not helpful.
Like I can invent ACs for the enemies too, yet MM actually lists them. Controversial opinion, but rulebooks we pay for should actually provide the rules.
Different thing. But if you want to play that game: the DM can just decide the AC. Increase dex of the monster, change the worn armor etc.
And yes, they can't be exhaustive and GM needs to make rulings, but providing rules for simple things and benchmark that help the GM extrapolate consistently are a good thing.
I don't mind some DCs. Xanathar's guide has some DCs for tool uses. That is useful.
And of course it makes things more newbie friendly.
If those examples are useful and have a good range. What I wish for is having some typical applications for a skill listed for each DC:
Lets mak an example:
Athletics:
DC 5: climb a ladder at fast pace, swim in a quiet lake without clothes.
DC 10: swim in a stream, jump on a small table.
And so on.
So instead of making an exhaustive list of tasks with DC's I'd like it to be sorted by DC and some examples so a DM can get a feeling for probabilities... most DM's make every check on step too hard.
Maybe have a big box with an explanation why making checks too hard sucks. How it leads to powergaming and so on.
A lot of us here have decades of experience,
... and still they make the same errors over and over again...
but there are people who pick up these books as their first game, and "just figure it out" is not helpful advice for a person in such a situation.
Which I never said that it should be that way. But giving 100 tables to look up useless DC's is not helpful either.
It is more helpful to adress DC's to checls on the fly based on the felt difficulty. Which is always very circumstantial.
And it is more helpful to teach them not to describe surroundings in exact numbers. Big room, small hall, a wide chasm...