I won't repeat all of the reasons -- they have been repeated here many times and are self evident.
I know you aren't alone in your sentiment, but I've never disagreed with a (vocal minority) segment of CB as much as I do on this.
Taysom is a once in a generation talent. Tanner has a chance to be great, but he has a variety of bad habits and last year often played like the freshman he was. A year backing up, and likely getting some PT along the way, would be great for his long term development.
This isn't a hard one.