Why don't cryptocurrencies create inflation if there are so many of them? One of the advertised advantage of bitcoin is that it can't create inflation. Governments can't print more money because bitcoin is fixed at 21 million.

But how about creating other crypto currencies when 21 million bitcoins is reached? There are at least a thousand crypto currencies in existence now. Isn't that a form of inflation? You are creating more money although not of the same type.
Other crypto currencies are their own entities, like each country contains their own currency each crypto currency is self contained. While others (fiat currency) depend on the rise and fall of the US backed dollar. Other coins aren't hinged inherently on the rise and fall of bitcoin, these coins depend on their own usage, efficiency, or adoption. 

More reading here. 
https://www.coindesk.com/bitcoin-explained-global-currency-wall-street-veteran/