Just taking a stab in the dark here:
Suitable would vary with conditions and non-normal requirements eg pax facilities, instrument approaches, fire cover etc etc etc.
Stupid example:
Non towered airport with 12,000 runway and no terminal or air stairs that fit your aircraft.
Yes, suitable for “we need to get on the ground NOW” followed by evac by slide.
No, not suitable for a weather deviation ‘suitable airport’.