At this point, he is still an unproven talent that the Chiefs are hoping can show promise and potential in his rookie campaign. According to Adam Teicher of ESPN, this had played a significant part in his decision to not take on endorsement deals yet as his agent Leigh Steinberg stated that his client first wants to prove himself on the field.
“I talked through with him the process of maturation and process of integration that many of our quarterbacks have went through, whether it was Troy Aikman or Steve Young or Warren Moon,” Steinberg said. “We talked about how the first year the goal was to integrate into the team, and the only way to do that is to pay deference to the incumbent veterans and try not to go into the situation with a high profile.
“We intentionally didn't do endorsements that would run in the Kansas City area even though they were offered. We didn't want him to be on billboards and everything when he wasn't even playing.”
This is an approach that not many players have typically taken given that endorsement deals are a big part of garnering more money outside of the league along with helping to grow his popularity. However, Mahomes wants to first show that he is deserving of those opportunities.
The Chiefs have remained quite high and optimistic concerning his future prospects given what he has shown in his limited action on the field. In his lone start in Week 17 last season against the Denver Broncos, he showed much poise and confidence in his ability by completing 22 of 35 passes for 284 yards with an interception in a 27-24 win.
Mahomes has shown to have a tremendously strong arm that could help him along in his development in his second year to become a franchise quarterback
What this decision by him to not take on endorsements at this point shows is that he has the personal drive and motivation that is needed to find success at the next level. It's now on him to demonstrate that he can do just that.