I think it is done to prove to everyone they are on the job on time. They then have a longish break around 9 a.m. to compensate for the early start. I am surprised that you don't mention lunchtime though. Around here, we get a repeat of the 7 a.m. racket from
1 p.m. until about 1.30 p.m. (when Mums with small children have given up trying to get the youngster back to sleep again) and then maybe a quick burst at 5.30 p.m. or even 6 p.m. to show us they haven't gone home yet...
Mind you, having waited for days on end for workers to turn up just in time for their 11 a.m. break in England, I think I prefer the 7 a.m., 1 p.m. 5.30 p.m. routine - and sometime or other they get tired of annoying us all, finish off the job and go away for a few weeks.