Why are some ATP CTP providers not on the FAA's approved list? The FAA has published a list of ATP CTP provider schools. But I can still find other schools not listed in this list, like "ATP flight school".

I'm sure that only approved facilities can provide an ATP CTP course. What's happening here?
The FAA's ATP-CTP Advisory Circular 61-138 does not prohibit a qualified ATP-CTP instructor using an approved training program from delivering the training at any facility that is willing to pay for their services.