They know they aren't going to get caught. Roads in the area are really popular as training routes, even Bradley Wiggins used to train round here, but the behaviour is appalling and the plod have zero interest in it. The dual carriageway that I used to live next to is used on Wednesday nights in summer for time trials and it's carnage. The club officials are total arseholes, they'll block junctions so cars can't enter the dual carriageway, they'll block the gaps for right hand turns, they'll stand in the carriageway with flags to force vehicles into the outside lane, they'll jump out at vehicles at the roundabouts either end of the loop they race on (one of which is a motorway exit). Loads of near misses, loads of complaints from residents. I never once saw the plod on the training nights. The irony is there is actually a separated bike path either side of the road.
Where I live now isn't as bad but still a pain at weekends. I've had people in my front garden watching club cyclists (presumably some race was on), the road at the top of the hill is regularly blocked with cyclists gathering en masse so they can bomb down the hill in a group. People complain all the time. I'm yet to see the police ever interfere in any of the races or time trials when the times and dates are known. No chance of catching random bad cycling behaviour.