Of course he may eventually look to Hardman and get him the ball, the point is time and getting him to do something he doesn't want to do. Kelce and Hill had 22 targets in the game, Hardman just 1 target (and the other WRs combined for 8), so no surprise he looked there first and the Bills were giving him what he wanted.
On the special teams, the Chiefs average 23 yards per return, and returns take 5-7 seconds to play out, so if you kick it to the 5, you're expecting to give them the ball around the 30 with 6-8 seconds which is time for 1 play and maybe a second or two left for a FG attempt or a hail mary.
It's also the only chance to burn clock without giving Mahomes and Reid a say in what's happening.
And no, obviously you can't guarantee anything with that, and it's possible they have a bigger return, or he still finds Kelce or Hill for a 25-35 yard gain with their one play, but it's about giving yourself the best chance to win and limiting the other team's options. Instead, the Bills said, "Here, Chiefs, you decide how these 13 seconds are used."