It's not an excuse. The fact is that Freeze has no end duration. There's a chance each turn you will thaw, but there's no cap to the number of turns you can be Frozen. By contrast, Sleep will last at most 3 turns. There are also a number of ways to play through or around Sleep -- moves that can be used while Asleep, moves that will wake a sleeping ally (or enemy), on top of Berries and medicine. For Freeze, only Berries are a defense. Sunny Day will thaw, as will being attacked by a fire move, but those fire moves are most likely hard-hitting offense moves.
It used to be much worse. Sleep used to not have a cap on number of turns. And Freeze had no chance of thaw.