There are a thousand and one subjective reasons why a goal that was given by the on-pitch ref can and have recently been disallowed after review by the video pedants.

Even offside has subjectivity, something we only discovered after we implemented video review. Could you accurately tell which pixel of shirt sleeve is an attacker's arm and which is shoulder? (Your arm can be offside because you can't legally score with it, shoulder vice versa)

We already have goal line technology for the ball crossing the line, it's totally instant, the ref has a device on his wrist which vibrates.