If hundreds of commits are baked into a software - under an open source license but without the full copyright transferred to a central legal entity - then it becomes impossible to change the license post-hoc.
3 clause BSD gives everyone permission to use it in new works that are made available using license terms of one’s own choosing, so long as the obligations of those 3 clauses continue to be met.
But what I get from this is: The project switched away from 3 clause BSD to something that is less permissive.
Licenses like the GPL come with an obligation that one not add restrictions when passing the software on to others.
If you care about a software commons, if you care about benefiting from the improvements others make to your own software, if you care about your users benefiting from the improvements others make: use a copyleft license!