Actually they hire a lot of average joes in music videos. Most music videos tend to hire models rather than actors because its mostly just about posing rather than playing a role. Im not sure how sam being in a music video is "Acting credentials". Lets be real, if he wasn't Britney's boyfriend he wouldn't have got any of the roles he has now or are upcoming for him. They would have hired someone who actually knew how to act. And that is one of the effed up things about the entertainment industry at the moment, producers care more about hiring people with good looks and clouts versus people that actually have acting credentials. There are a lot of talented young men and women on broadway that actually have "acting credentials" and they are getting paid pennies while being passed over for people like Sam.
The reason people have a problem with Sam is based on his past of horrific social media posts, his history of dating older woman more famous than him, and Britney's history in choosing men. He also doesn't seem genuine in interviews and has this vibe of being completely rehearsed for the cameras.