It's a few different things combined:

• Competent host: Sean Evans seems like a perfectly normal guy with above average charisma that isn't as manufactured as Fake Laugh Fallon or Waitstaff Abuser Cordon. The team also seems to do their research in terms of guests and tend to ask questions they didn't already just answer in another interview

• Novel premise: Instead of the host asking raunchy or off cuff questions, the host asks mundane albeit obscure questions regarding the celebrity in question loses composure due to increasing spice. A part of the spectacle is seeing someone famous lose composure in a way that isn't in a public mental breakdown or substance induced rampage.

• Generally wholesome: Or at the very least not mean spirited. Despite some dramatic sound effects added after the fact, the show is actually extremely benign and doesn't antagonize anyone. Fairly accommodating, if the interviewee is vegan they'll have vegan wings, if they don't eat processed food they get like fried cauliflower.

I get the appeal and have seen like 4 or 5 episodes.