The new sidewalk was nice and winding. But it had a problem that needed to be repaired. And because it was in a public place, the crew had to stay and wait until the new concrete dried before leaving to ensure there was no damage.
Whether intentional or not, people can create a lot of damage by entering areas that are not yet meant for use. They like to check out new things. Whether it is a new facility, or new systems, or something that is not yet complete, having clear boundaries that are respected by people is necessary to keep costs down and maintain functionality.