His character is not one to take shortcuts or accept handouts.
He is a tweener, he will act smug and even heelish during matches and segments but he will not do anything dishonorable (like cheeting) nor attack the crowd.
Well, he does down low shoot on certain crowds, see Philly: "I won the Royal Rumble right here in 2015 and went on to main event WrestleMania two years in a row...so this sold out arena right here? This is my house now." For the fans in Philadelphia that was equivalent to throwing that in their faces just like he would claim a win over an opponent and insult them with it.
I don't interpret his character as caring so much about honor like a wrestler such as Kalisto obviously does, he did cheat Braun out of a title in a tit-for-tat situation, where the honorable thing to have done would be to ask Mick Foley for a title shot no matter who won between Strowman and Owens. In kayfabe Foley favored Reigns to a degree that he'd have every expectation of getting that, too.
I see it as Reigns being too 'good' to cheat in the same way that Brock is. He doesn't cheat to win because it would lower him. It's not a moral issue, it's that fact that losers cheat because they can't get the job done and he's a born winner.