Ryback left WWE because he didn't like the way he was used and treated in WWE. According to him, he was promised to become the heel of the company if he stuck to the script. He didn't feel WWE was living to their own end of the deal. He was used most for pre shows and not for main events. He stated that the taxes and travel expenses take up large part of what he makes from WWE. He believes WWE should take up some of the travel expenses.
Ryback started his own podcast since he left WWE. He revealed most of these things in his first episode titled "Conversation with the Big Guy".
There are a lot of WWE fans who are familiar with Ryback and were disappointed when he decided to leave. Since he left, he has started making his own podcast. He wanted to tell people how he was feeling. Not surprisingly, he talked about the reasons why he left WWE. He said that even though he has a huge contract, the expenses he has to pay for and the taxes are not worth it.
The promise was he was going to be the new heel of WWE but when the booking started, he was tasked to do the pre-show and not become part of the main event. That was when he decided that he would leave.