I think its a risk between a few factors.
1-Peyton's health is not necessarily set in stone so nobody knows.
2- Thomas seems to be to get a high number of the looks in the offseason.
3- PEyton does favor the TE at times, so I think thats probably the most value in the offense.
4- People dont believe in his physical tools to be a consistent threat.
I think that if he ends up in a Welker role then he can be deadly, but he just doesn't (in my eyes) have the physical tools to be able to be that successful. A lot of his success last year came not because he was out matching people but because he was out working them on broken plays due to poor qb decisions. Thats just not there anymore.