There are a few & they become obvious once you start looking at past editions.I do not see any such barriers that make it difficult for a DM to add or subtract skills in the game. Might just be DMing style, but I have had different skill lists as well as used the Variant Ability Score variant rule for skills for every single campaign of 5E that I have run and have had no issues.
So I do not believe there is some systemic issue with the game as presented, but rather that individual DMs have styles which run counter to the skill system as presently constituted. Now of course that doesn't HELP them in any way, shape or form... the break between the 5E system and their DM styles will probably never reach an accord the player ultimately is happy with... but the game itself is not broken across the board. And we know this because some of us can and have been using the system without a problem-- either as-is or by making our own desired changes.
5e
3.5
2e
Not including the 4e sheet because I didn't play it enough
3.5
2e
Not including the 4e sheet because I didn't play it enough
They didn't stop there though & I linked to an example from this very thread of presented barriers in the post you quoted. Wotc included the ability score associated with each skill & a box to precalculate the combo despite creating a skill system where the GM is supposed to call for an ability check which the player can make a case for why a particular skill proficiency is relevant enough to add the PC's proficiency bonus to the d20+called for attribute mod to the check. All of that creates friction for the GM if they attempt to call for an ability check & have the player ask if a particular skill proficiency should be added instead of simply calling for a particular skill check from an overly narrowed skill list.