Marine protected areas often look to take care of species that don't move very much. Can migratory species which can travel vast distances benefit from protected areas as well?
If people keep fishing inside the no-take zone, it doesn’t really meet the criteria of being no-take. Inevitably a fished zone will fail to meet expected successes of a no-take.
Marine protected areas differ if how much protection they offer, and some may in reality not offer much more protection than you get in the rest of the ocean anyway. Why does this happen? Politics.