I'm sorry to undercut your snarky aside, but "myriad" is used metaphorically to mean "many" or literally to mean "10,000," the same as "dozen" is used to mean "12." It might be that if you add a lot of apples to a lot of oranges, you have a (bigger) lot of fruit. And you can use "myriad" in this way. But used literally, "myriad" is like "dozen." You can have several dozens of things, and if you have 30,000, then you have myriads.
I'm sorry to undercut your snarky aside, but "myriad" is used metaphorically to mean "many" or literally to mean "10,000," the same as "dozen" is used to mean "12." It might be that if you add a lot of apples to a lot of oranges, you have a (bigger) lot of fruit. And you can use "myriad" in this way. But used literally, "myriad" is like "dozen." You can have several dozens of things, and if you have 30,000, then you have myriads.
Yes, it was mostly intended to be snarky. But I also personally just don't like the noun form. It feels archaic.