your characterization of what happened with him at Auburn is simply not correct.
boosters at Auburn ousted Malzahn in order to get Steele hired as HC, primarily because during Steele's entire tenure at Auburn the defensive was miles ahead of the offense. this was reported in an
AL.com story:
In his fifth year as Auburn’s defensive coordinator, Steele had culled support from those influential boosters over the years and boosted his stock in their eyes through his unit’s strong performance on the field. He “badly wanted the job,” according to a source, and would quickly accept an offer.
The plan was set: Fire Malzahn on Sunday and announce Steele as the next head coach within 48 hours.
Steele was named interim coach but ultimately the boosters that wanted him as Auburn's HC lost a power battle with the AD, who wanted to conduct a national search and ended up hiring Harsin. it's all in the AL.com story I linked to.
to say he "could have been retained" at Auburn makes no sense. there was no way that Harsin was going to retain a guy who had potentially gotten the previous coach fired and had all the biggest boosters at the school trying to get him the HC job.
he was then hired at Tennessee, but Pruitt got fired shortly after due to NCAA violations. Steele was named interim coach there, and when they hired Heupel he wasn't retained. then he sat out for a year. the timeline is all there to read about if you have any interest in doing even a basic bit of research on this.