Why are people getting vastly different rewards?

amge taken from google

Steemit is not a "get rich quick" scheme. While it is possible to post content that goes viral quickly and earn a lot of rewards on a single post, this is not typical for most users.

Most of the authors that you see earning high rewards are users that have spent a lot of time in the network building followings, making connections with others, and developing a reputation for bringing high quality content.

It is best to have realistic expectations, without focusing on rewards when you are first starting out. Work on building a following, making connections, and developing a good reputation. Consistency will pay off in the long run.