The Standard Model Doesn't Allow the Neutrino to Have Mass

There's no reason the standard model couldn't have four or seven generations or 90,000 generations of particles. But it's an interesting clue when people wonder, like, what does it mean that there are three? Is the universe like three-ish? Is this just what it is or is there a reason for it? Another really fun mystery is neutrinos, right? Neutrinos are part of this basic list and we know they exist and they're out there and there are three kinds of them but we really don't understand their masses.