The public perception of a cryptocurrency has big bearing on the value of the currency.  In the case of Bitcoin, a driving factor can be people reacting positively to the innovations and the fact it is a thorn in the side of the mostly corrupt banking sector and gives competition which cannot be tampered with in the traditional way.

Many cryptocurrencies are not known in the public eye bar a few and the smaller ones typically have a cult following, so their prices are much lower than say Bitcoin, Litecoin and Ether.
Many cryptocurrencies are reusing the Bitcoin code and just changing some of the specifications such as the coin supply, proof of work algorithm or adding other features. How much a currency has ripped off of Bitcoin with no innovation or potential utility over Bitcoin can affect its reputation.  Thus people themselves are the cause of growth.

Also, factors such as: difficulty level(mining),supply/demand,scams.