Comey is only 4 years into his 10 year term. I trust that Trump felt comfortable with him and keeping him on (he could have fired him). Probably looks better for Trump that he kept him on. Plus, Comey should know where all the “bodies are buried” so to speak, which may be helpful.
Hopefully the higher profile of staying on will also provide an element of protection for him, as opposed to dropping out of the public eye.