Lot's of dependencies are used that they do not own the rights to do this with. Not practical.

What about documenting the requirements to rebuild it from scratch? Not trivially done, but these are exactly the types of games that attract the people willing to put in the work.

Publishers may wind up spending money and diverting resources just to give their IP away to people who might otherwise be customers for new properties.

Typically not so much on the servers. And in nearly all cases a "no third party proprietary code" server requirement is very feasible.