It's not clear to me why ground wires aren't subject to the same rules as neutral wires (one per bus bar hole). What's the reasoning here?
Grounding conductors are designed to only carry fault current, which is typically a very short burst of very high current.
Neutral conductors carry circuit current, which means they go through heat/cool expansion/contraction cycles. Multiple neutrals under one screw can lead to loose terminals due to different rates and levels of expansion and contraction.
It all boils down to isolation.
Say for example, the electrician needs to troubleshoot a circuit. By isolating the neutral in its on screw there is less chance of interrupting critical/sensitive power elsewhere because the circuit is isolated.
Otherwise, the electrician would have to kill multiple circuits to troubleshoot. Even with a redundant power supply setup ( used in telecommunication racks ) if the neutrals where joined together as grounds where, then the redundant system would be compromised.
The industry already has dual tap breakers. The reason the industry hasn't come up with dual tap neutrals is not because the can't, but simply the financial harm it would cost when Joe Electrician pulls the wrong neutral where 10 seconds equals tens of thousands of dollars in business losses.