I think this has to do with having the right build for football but having going undrafted motivate the fuck out of you to get good enough to make a team. And it's people like that, who have good work ethic, that can surpass more naturally talented but lazy players.
yeah scouting is definitely part of it. But I'm just saying to make a team from undrafted (and not play just special teams) you need to be highly motivated most likely