Just so you know you made me pull out my Player's Handbook just to make sure I wasn't talking out my backside. (p. 175 in case you're wondering)
It's a Variant rule that allows non-standard use of Abilities with a skill that isn't their associated Ability. Variant rules are really down to the DM's discretion with player's consent. Usually before they start playing a game and around session 0 when everyone gets what kinda play style they want and any home rules that everyone agrees on. As in: not suddenly out of no where does a DM rule that no it's an Arcana + Dex check with any proficiency out of nowhere and you feel singled out because that was your dump stat.
I personally think as a rule it's a good one to have, granted it makes sense for the scenario (like people above stated, Stealth + CHA for blending in a crowd or Athletics + CON for a long swim are awesome examples.) But it should NOT be "oh I like because my players stats get a bonus" or "boo I don't like because my dump stat." The whole point of getting many options in a computer game is because code is limited to whatever the people programming can think of. And they can't think of EVERYTHING, so they have to try to give us, the players, as many options as possible and/or make a system that allows flexibility.
So yeah, over 80% or so (a number I pulled out of my wizard's hat) of the times you use a skill it should be the stat it's associated with. But some moments will call for nonstandard stat and skill combinations, like maybe acrobatics + CHA to pull off a backflip with some flair to show off. And that's okay. To me, anyway.
So, is it a bug? Or is it a feature? I dunno.
