Your threat exposure is not just your network. It's all of your customers and all of your vendors as well.
Recall that the Target POS hack back in 2014 happened because someone hacked the largest refrigeration contractor in western Pennsylvania, then bounced from there onto the Target Partners Online portal with legitimate credentials, and then from there in unspecified ways got onto the POS system. Obviously going from TPO to POS is a failure of Target's network security, but their network perimeter was much larger than just Target computers.
Recall that the Target POS hack back in 2014 happened because someone hacked the largest refrigeration contractor in western Pennsylvania, then bounced from there onto the Target Partners Online portal with legitimate credentials, and then from there in unspecified ways got onto the POS system. Obviously going from TPO to POS is a failure of Target's network security, but their network perimeter was much larger than just Target computers.