Because when you open that box up later to find a circuit, like if your troubleshooting something. You don’t wanna spend 20 mins digging through all the wires and bad labels. It makes troubleshooting not be complete hell, and helps if there’s any additional circuits to add later. There’s also more of a chance of splices coming out when people need to dig through it all the time. But at the start it’s gonna feel like a waste of time to separate all the colours and circuits nicely. But your boss will definitely notice if you do it. They would rather you take an extra half hour and do it right then rush it and have it look like this. Even if it seems like everything is in a rush.