10 speeds and 11 speeds are common.

But the 10 speeds of today are not the same as the 10 speeds you're thinking of. The 10 speeds of today refer to the cassette ... there are 10 gears in the cassette.

As for the chainrings, there are a few options ... single, double, triple, compact.

So what you know of as 21 speeds (7 x 3) are a thing of the past (like a decade or more ago) and what you are thinking of as a 10 speed are a thing of the distant past. It's a whole new world!