[sobellian]

The historical rules also left ambiguous promotion to the opposite color: https://chess.stackexchange.com/questions/8291/pawn-promotio.... This rule was clarified later to restrict to the same color.

[CSMastermind]

> The player’s choice is not restricted to pieces that have been captured previously

I grew up playing chess but my grandfather always insisted that pawns could only be promoted to captured pieces so when I played him we had to play a that variant.

I suspect this came from players not having extra pieces with their chess sets.

[vitally3643]

That and just avoiding the obvious advantage of promoting every piece to a queen every time. Puts more constraint on the game which usually makes for more interesting play