Seems really basic to me, but I have zero knowledge or experience in this sector so maybe I'm missing something?
I have actually arranged evictions for a social landlord, admittedly some time ago. In most cases the property had been vacated, so bailiff attendance was a legal formality. Where the tenant was still in situ, and particularly if there were children present, the bailiffs would sometimes postpone in order to avoid unpleasant scenes. The one case I dealt with where the police attended and did the breaking in and removing the tenant had been pre-organised as a result of intelligence about them. I was out of the loop on that, and was just informed that it was going to be done that way, so don't know if it originated from police or bailiffs.
My guess would be that in at least some of the cases we see, the police are not aware in advance that there is likely to be a confrontation, and are reluctant to carry out an unplanned operation with a volatile crowd milling about. It may be that this represents a failure on the bailiff's part to inform the police in advance that trouble is likely. In my day, bailiffs would carry out pre eviction visits, and if this is still the case, you would have thought that the presence of mad notices about rights of access and the reaction of the evictee would have led to them requesting police assistance in advance. Mind you, perhaps they do and the police say they don't have the resources?
Incidentally, I can't recall seeing an agent of the organisation repossessing the property on these videos. I was always present at our evictions - it was us who booked the locksmith. Perhaps the problem is at least in part that there is nobody on site with an interest in the eviction going ahead. The bailiffs don't really care one way or another as they still get paid, and they'll be paid for re-attendance.