I can understand why. For me, it helps to think of it like this:
Minions don't really have 1 hp. They really have as many hp as they'd have. Their HP totals are just so low that, as a simplification, we're saying 1 hit from the PC's of about the same level kills them. The game is just telling me "the HP is just too low to worry about."
If I really wanted to, I could, perhaps, give them hp. 1/level, or equal to their CON score or whatever, they could have it.
They'll still die in one hit from a PC.
If I'm using a minion outside of their intended use, I think I'll translate that 1 hp into an actual total, but 90% of the time, "one hit kills them" is going to be true no matter how much hp they have.