I think it goes back to the front office. Either their scouting department is horrible or the general managers they've had over the years can't spot talent like those in Kansas City, Los Angeles (yes, both the Rams and Chargers), New England, and, dare I say, Tennessee. There's a reason the aforementioned franchises are enjoying success as of late, and one of them practically had a dynasty that lasted off and on for twenty years!
Coaching matters as well. Andy Reid is one of the greatest offensive minds in the game today. Let's not forget he almost beat Tom Brady and the Patriots fifteen years ago with Donovan McNabb, who isn't exactly touted as a former superstar quarterback. (Was McNabb talented? Yes, but he wasn't as good as Patrick Mahomes is.) He was gonna win the Super Bowl eventually. He just needed the right quarterback. Enter Mahomes. Kansas City knew he was talented. They knew he could be great, especially if coached right. And he fell into the Chiefs' laps. The rest, as they say, is history.