[qftlzhut] why does M87* rotate?

"Measurement of the spin of the M87 black hole from its observed twisted light", Fabrizio Tamburini, Bo Thidé, Massimo Della Valle.

the collisions and mergers which built M87* happened at random angles, with objects of randomly oriented angular momentum.  the random rotations should have canceled out.  some hypotheses why not:

1. local universe in the region of M87 has angular momentum
2. small random excess angular momentum turns into huge spin rate because of black hole compactness
3. black holes prefer to eat things that are rotating in the same direction
4. angular momentum is not actually conserved