Many sources (including here, here, here, and here) explicitly list Royal Flush as the highest poker hand. This seems unnecessary - it's the highest hand anyway as the highest Straight Flush. When designing a ruleset, unnecessary is harmful (e.g. it gives new players more to remember). So is there a good historical or game-mechanics reason why we treat the Royal Flush as a special case?
I don't believe it has any historical background other than this is how the rules go.
A royal flush is the highest hand possible and is given a unique name as something to achieve.
I got a royal flush sounds a lot cooler than, I got an ace-high straight flush. It feels more prestigious.
I also don't find it confusing, and if it is, it's a quick explanation to set the person on track.
It clears up that the ace is the top end of a straight
2 though 10 is clear to anyone that can count
It clears up the top end is
Yes it is obvious if you play poker but if you don't know the game at all it clears up some important stuff
Also the math is a little different as a royal flush is actually easier to hit than others. The ace is block on a king high (it becomes a royal). Where there are not over blockers on ace high.