Because ethereum is not the same as bitcoin. It has different code in it. As everything is programed by human you can tweak every little parameter in your code. How you do that at first? Simply for the code base of bitcoin and tweak it's parameters such ethereum made blocks to come every few seconds while with bitcoin blocks appear every ten minutes, see the difference? It is moving faster and putting transactions all together which makes it cheaper. But again ethereum had much more transactions due to smart contracts working all over the place so they would have to implement such thing either way. However bitcoin devs don't clearly want such thing to happen with bitcoin....