He didn't have a degree until last month, so he wasn't eligible for an assistant coaching job. Cal created something for him at UK as a student assistant and now created something for him at Arkansas. He couldn't just apply for or show interest in an assistant position because he's not eligible for one. In order to be a full-time assistant coach at the college level, you need a college degree.
He was literally a student employee for Cal so probably made next to nothing. When you type in "Tyler Ulis Arkansas salary" in Google, the first thing that pops up is, " Tyler Ulis is an assistant coach for the University of Arkansas men's basketball team. He is not paid a salary for his role with the Arkansas Razorbacks."
Now, if he sticks around after this year, then I'm on board with questioning his decision making. But now that he has a degree, I would bet he looks for a full-time gig outside of Arkansas before next season.