Part of it is out of their hands, but it is stuff that matters.
Patriots first 3 SBs:
2001 - Snow game v. Raiders, v 13-3 Steelers, v. 14-2 Rams a/k/a "Greatest Show On Turf" w/ HOF QB Warner
2003 - v. 12-4 Titans, v. 12-4 Colts w/HOF QB P. Manning, v Panthers
2004 - v. 12-4 Colts with HOF QB P. Manning, v. 15-1 Steelers w/Roethlisberger, v 13-3 Eagles with Andy Reid
Chiefs first 3 SBs:
2019 - v. 10-6 Texans, v. 9-7 Titans, v. 13-3 49ers w/ JAG choking away the game
2022 - v. 9-8 Jaguars, v. 12-4 Bengals, v. 14-3 Eagles
2023 - v. 11-6 Dolphins, v. 11-6 Bills, v. 12-5 49ers w/Brock Purdy
So Brady/Patriots were playing against much better teams and much better QBs. And Mahomes/Chiefs is 1-3 against Burrow and Brady in the playoffs. Really, the Chiefs have only had one decent SB season run (2022), with 2 seasons against weak competition when better teams would have almost certainly taken them down. The Patriots, meanwhile, had 4 wins against QBs who either are already in the HOF or are locks to get in during a shorter (4 seasons v. 5 seasons) stretch.
So the Chiefs are not frauds, but they're wildly overrated by themselves, their fans, and the media, and a lot of serious football followers who are not Chiefs fans see through the hype.