Maybe, the bouncers have faced similar or worse experiences before where random "tough" blokes take a swing at them or worse and finally snapped?
If they had not reacted, do you think those two idiots or others like them would face any sanction or punishment?
Of course, their reaction was excessive and they will pay for that at least professionally, but what you see in a single video is not neccessary a true picture of reality.
Well, I faced that 'reality' many times, myself.
I can't speak for anyone else, but after years of 'watching and learning' I decided that if I got the chance to head my own team, I would do things differently.
So, when I did, I told my team to let me know if ever there were any 'problems' before deciding on their own course of action.
For me, I would take the 'loudmouth' or the 'head guy' of any bunch of lads and tell them where I stood and where the club stood in order for people to enjoy their night out.
I was up front about choices; control your peoples or don't come in.
I found that garnered a lot of respect that I was prepared to give them a chance rather than be knocked back.
Any issues and I tended to isolate potential trouble makers by needing to 'speak to them outside', then not doing and asking them to wait.
Eventually the guy's pals would coming looking for him one by one and then they were all out.
No aggro, no punches, just annoyed parties who had their enjoyable night cut short and they fooked off somewhere else.
Many times I had my hand shook for not starting fights and sometimes not.
So, yeah, you don't have to be a knob to work the door, knowing you can hurt someone.
Just set your boundaries and treat people like Human Beings.