American Alpha did not flop. They were actually gaining a fan base. Just because WWE decided to essentially write them off is not them flopping. They were the most entertaining tag team on Smackdown and usually always got the crowd into their matches.
Now.. Bayley flopped. She's been given chance after chance and push after push and hasn't improved at all. Her promo delivery is that of freshman in high school giving their first public speaking speech.
The problem with American Alpha was the fact that they were BUILT in NXT - the whole story of Jason Jordan not finding suitable tag team partners, Gable coming along and being his partner. Them winning the crowd over with their impressive ring work, FINALLY winning the belts and putting on match of the night performances every time they wrestled.
Suddenly, they're on the main roster, they don't HAVE that story. In fact, American Alpha are living proof that wrestling is bottom of the barrel when it comes to caring about someone. They don't do enough talking. Gable is impressive on the microphone but they don't let him speak. At this point, they may as well just turn heel out of frustration with Gable saying how him and Jordan are elite athletes and how he is an Olympian and they get absolutely no respect etc.
NXT tag teams flopped on SD. Because SD doesn't know how to book their tag division, nor do they actually care to. I mean I believe SD went a solid 2 weeks without featuring their tag team champions. That's unacceptable.