What "on site"? The various valves that need to be controlled remotely often are just a box, perhaps even underground, in a place where's no buildings for people to stay - a mechanical team can access the hardware on-site, but building and maintaining an actual office on each site is not practical. The same applies for power grids - you can't staff every substation with people.

A remote operator can manage dozens of such sites, a single "local" person might be close to one point, but the next control point is going to be miles away, so you either need much, much more people to station one at every valve, or have a situation where flipping a switch in all the "sites" is very slow because requires the "local" person to drive many miles visiting each location.

No, there's a reasonable objective need for this management to be actually remote - there's a discussion on how this should be implemented in a secure way, but it does have to be remote.

Many sites are in the middle of nowhere so it is inconvenient to go to them, so accessing them over a network saves a lot of travel time and cost.