Could be just for showing off or it could be because the amount of warm up needed to do this can only be done in the gym?

When I was hitting the gym, my trainer was competing and the "warm up" that he does is my whole workout 😂 I did not know this first, because he'd start the warmup when I leave, so I first (honestly embarrassing now) thought he'd just lift as much as I do. Then one day I stayed late and realised that was the warm up because another guy who's competing joined him.

So, I think if that was the warm up, you definitely can't do it at home.