I think that many things come into factor including:
Familiarity: there are still many out there who are not familiar with alternatives to AA
Ease of Access: There are many more AA meetings
Service work/Outreach: AA puts a big emphasis on service work. Volunteers take meetings to hospitals, rehabs and other institutions. Other programs do not put such an emphasis on being of service to other alcoholics (with the exception of Celebrate Recovery).
I think Fini nailed it
if people want LR meetings/options in rehab centres, those who have used LR as support need to give back and make that happen by putting in the footwork.
I did not go to rehab but when I decided to get back in recovery, I knew where AA meetings were located. I have been drifting lately more toward mindfulness and Refuge Recovery which at this stage of my journey is a better fit.
If it was not for someone posting about it on SR, I would never even have known of its existence.
I knew of Women For Sobriety (my sponsor back East attended too) but they meet only once a week in one location and they really don't do any outreach.