I think the reason is that the gas people dont fill in the hole straight away is that they have to monitor the repair for about a week to ensure that there are no further leaks.

I had to have a new pipe from the road to my property a couple of years ago and tha same thing happened. The hole in the road was left for about a week and a chap turned up every day and had a check around the hole and right up to my house. They don't actually fill the hole themselves they have a dedicated team who do this. They took pictures when thay had finished presuamably to prove that they had done the job.