Nothing but pure speculation, so ignore if you aren’t in the mood:
Rumors has it this was an older,very experienced, near pension age captain with a quite fresh co-pilot.
What if the captain had a medical event gradually getting to him on approach? Reverted to experience and aimed for the old airport, realising his mistake but was incapacitated, out of energy and unable to correct the situation or transfer control. Even with the best CRM in the world, that could be a tricky situation with such a cockpit gradient?