OK so I'll give you the benefit of the doubt and say you're not trolling. There are plenty of quite obvious reasons why people aren't annoyed at KO entering MITB:

• Kevin Owens is a heel. We're supposed to not like him. You've ironically pointed out that Reigns acts like a heel by making this very comparison, and proven that his actions make him unlikeable.
• Everyone knows Reigns gets preferential treatment behind the scenes and that colours their perception of him. People can't ignore that he's Vince's favourite.
• Reigns didn't just get a title shot, he actually complained like it was somehow a punishment to get handed an opportunity the rest of the roster literally is fighting to get. Expecting us to feel sympathy for someone complaining about unfair treatment, while they benefit from clear and blatant favouritism is not only bad storytelling, it's genuinely insulting. You can't just ignore reality whenever it suits you and expect everyone else to play ball.
• Kevin Owens never got his rematch for the Universal Title.
• Getting in the MITB match is still kayfabe much less of an opportunity to win the title than a straight singles match, as you have to beat 5 other guys in a brutal ladder match, then fight for the title. If we're talking the opportunities wrestlers are due in kayfabe, then going by WWE's own rules they still owe Owens more.
• We've seen Reigns vs Lesnar too many times. The title scene desperately needs someone new.
• You said it yourself: Owens has a lot of fans. And that's for a reason. He's just a better wrestler. He's a better and more interesting worker, he's miles better on the mic, and he's got an interesting character that we want to see put into situations like holding MITB, all without being pushed in bad ways. It's OK to not like him, I'm not here to police who people should or shouldn't like (unlike you...) but in a fair and balanced view of wrestling it's very hard to argue that Reigns is better.