Basically: The person who designed the crossbar solution was not having a good day. Or maybe was at his/her peak performance but would have been better placed at a different position in the staff hierarchy. The concept might have sounded slick when originally thought about, but having the enabling/disabling of one peripherial move the pin allocations for multiple other peripherials is a very hurtful design choice. Real life products have a tendancy to change during their life time.

A very, very good processor design would have had a full crossbar switch, allow new peripherials to be used without affecting any other assignments.

A good processor design might fail at mapping "any" signal to "any" pin, but would still consider one or more fixed options and either allow a new peripherial to be added or result in a limited collision that could be solved by just swapping one, two or maybe three pin pairs.

The design criteria of a simplified (non-full) crossbar should be to maximize the stability, i.e. minimize the result of any configuration change.