Why do we say

> 
> ***the French***
> 
> 
> 

to refer to the French people collectively, while we say

> 
> ***the Greeks, the Russians, the Jews***?
> 
> 
> 

Why ***the Chinese***, but ***the Tibetans*** and ***the Germans***? Why are some such nouns countable plurals?

We also say the "Soviets".