The reason that Europeans started traversing the Atlantic and also the west coast of Africa was because they were looking for passage to the East, which was rich in spices. Europeans previously got their spices from the silk road, but the Ottomans essentially closed that down. Asia was at the other end of the silk road, and so it conducted all of its trade towards the west. Also, The Atlantic ocean is quite a bit smaller than the Pacific.

They did sail around, Chinese explorers are reported to have landed not just in the Americas, but in Eastern Africa too during the XV and XVI centuries. However they didn't need to colonize like the Europeans. They had all they wanted back home, and they could cheaply buy everthing else. Remember that Europeans established colonies in search of (mostly) what the Chinese already had.