It's a bit like asking why a train can't simply stop when there's a car parked on the tracks.

I'm also just an outsider, but I'd imagine there's risks and costs also involved in stopping/starting production that have to be considered.

Shutting off oil fields probably isn't as simple as turning a tap. It's likely a complicated process that could potentially harm a site's future production. There might be problems or it might take months to get things operating again...