Are experienced operatives leaving the door supervisor sector?

The answer is quite simple to be honest, pay and conditions.
I stopped covering venue doors about 15 years ago and my charge rate then was better then than most venues are willing to pay today.
I paid all my staff as PAYE with all the benefits that that holds, and in turn I had great staff, then multiple shite training companies flooded the market with unsuitable under prepared staff who worked cash in hand for fly by night new security providers which drove the charge rates in to the ground.
That’s why proper Door Supervisors are walking away.

Totally agree with Premier's assessment. Why would quality people put themselves on the front line, keeping members of the public and the Clients' staff and premises safe, for low remuneration, when they can earn more stacking shelves?
The result is that those quality people are walking out the very doors they once manned and we are left with a woeful assemblage of inadequates who, quite frankly, are a danger to the public and to themselves. 'Two eyes, two ears, a nose and a mouth and you're in' seem to be the only attributes required. - All fun and games until someone loses an eye.