Because Briggs is ranked 46th and Wlad is only interested in fighting people in the top 10? If Briggs wants a title fight he should go knock on Wilder's door. Wilder loves knocking out old has beens.
Wilder would deserve just as much ridicule for fighting an ancient, roided, and shot to bits Briggs as Wladimir would get. Briggs has less than 3 rounds of stamina in the tank and has fought no one of note since staging his social media theatrics. We've already seen this play out five years ago... when Vitali almost replicated an in-ring casualty at Briggs's expense (October 2010). Briggs took one of the worst beatings since Holmes-Cobb. The man is pushing 50 now and can barely move for a sustained 90 seconds, ffs. He won't go near a legit top 10 guy and work his way into contention for good reason.
Maybe Briggs will get a shot at Wilder. Don't see Wlad fighting him unless Briggs beats someone in the Top 20. Briggs is about right for Wilder though. Wilder's camp shouldn't have anything to worry about as Briggs would probably tire early in the fight. Don't see Briggs rushing Wilder.
It would be embarrassing for Wladimir to fight Briggs. With Shannon's lack of recent accomplishments and current ranking, Wlad would be defending the fight to the media constantly during the build up and then would actually look like an idiot totally outclassing Briggs. It would literally be on par with some can crushing heavy weight fighting an internet troll in the gym, who's half his size, while wearing two left gloves. I mean, why would Wladimir want to look that ridiculous?