blockchain tech is still in development, but most of the cryptocurrencies are based on the original (bitcoin) which is the problem you will find in most places. The original bitcoin had a problem of scaling, where it solved so many other problems it introduced the scaling problem, and at the time the transaction cost wasn't one of the problems because it was a time where bitcoin wasn't worth anything, so who cares if you use 0.01btc on some transaction when you can get 500 for $2 or whatever. Now bitcoin is going into the tens of thousands of dollars each so the transaction cost follows along with that. There are plenty of cryptocurrencies that have tiny transaction costs, steem even manages to have zero transaction cost, but many of them use different technology so you will often notice exchanges only have wallets for coins using a certain archetype and are missing all the other ones, because they have to work with that specifically in order to have the coin on the exchange.

It's all a big convoluted disaster really, but there are many great things emerging from it too, like steem/golem for example :)