> Some developers really like to be left alone, and it's terrible for the business

The problem is sharing credit. What is the incentive for a good developer to share credit with a bad developer especially when the don't like each other?

If you do mob programming how would you know who is making contribution and who is slacking and how to rate the performance.

> The amount of outright hostility I've faced professionally for suggesting mob programming was staggering.

For a good reason. In my experience great developers don't mind helping out but they expect to be recognized which is fair.