Why don't cryptocurrencies create inflation if there are so many of them?
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/