Leif
Adventurer
What makes you think we don't get a saving throw each round?
To be fair, the save every round is a fairly recent addition to the spell. Back in the good old days, you only got one shot at saving against most spells, and if you failed you were just stuck for the duration. There is a notable exception to this that I recently read in the 1E AD&D PH, but I can't remember what it is. I think this makes the spell much less useful, particularly Hold Person, Mass, which is a 7th level spell that allows a save every round. Admittedly, at 7th level, the DC is considerably higher, but the target's bonuses to the save will be likewise enhanced, in all probability.