It’s more that it’s just more work for the DM in this case. Every time a skill check is called or considered, the DM has to reconsider if the character considers this a routine or trivial task. You can see this in the stats: if the character’s modifier is 5 or less than the DC, it’s trivial. But you also must consider even without a high mod vs DC, is this a task the character has performed hundreds of times before? I try not to come up with solutions, or utilize WOTC solutions that make a lot more work for the DM. Especially if there’s already a rule or slight tweak that makes sense and prevents this work: in this case, no crits for skill checks.
I suppose if the DM is running the game through a rigid preformed structure then yeah, having things make stuff more unpredictable is gonna be hard on the DM, but if they are already choosing to fly by the seat of their pants and roll with the incoming suggestions from the dice, it’s totally fine.
There are lots of different types of people that like to DM games. Something isn’t automatically worse for all DMs.
