Well, perhaps because it never was in that list?
All fouls used to only be fouls if the were "intentional." Over time it became clear that wasn't really how fouls were called. As I recall (but am too lazy to look up--the oldest I have handy is 2008-9) the very first set of Laws to drop intent for CREF had 7 CREF fouls (e.g., tripping, kicking...) and three that were not (holding, spitting at, and deliberately handling). I don't think there is any mystery as to why those three were outside CREF--they aren't really about being careless, reckless, or using excessive force. A trip or kick often comes from a clumsy (i.e. careless) challenge, but that just isn't how holds come about. Referees have long called the holds that matter, not those that are trifling.
Well, of course, pushing also occurs on CKs. the difference is that holding is generally an ongoing action--the player holding before the CK is taken is likely to still be holding when the ball is kicked, which is when it becomes a foul. A push is not an ongoing action. The direction to warn players who are holding is to avoid those holds continuing. (And, of course, nothing prevents referees from warning players who are pushing before a CK is taken--that just isn't the evil that the direction to referees is intended to stop--holding was the ongoing problem they were trying to address.
As to gaining an advantage, I don't really see any parallel. Seeking to gain an advantage was in the Laws and was reduced to gaining an advantage, which was limited to deflections/rebounds--there was no going back in that process, just the ongoing shrinking of what constituted active involvement. (Though I agree that the time came long ago where they should have cut the phrase rather than defining it to mean something at odds with the words.)