Claiming to be fully booked

Everytime i call to make a reservation for dinner, the manager claims to be fully booked. As I live in the area the centre is convenient for me. I end up supporting Riverside Bistro as they are a fantastic alternative. This restaurant is located directly opposite Erawan. When I am there I notice that Erawan have several open tables, which are not occupied throughout the evening. I don't understand why they have this attitude to taking reservations. For this reason I won't support them anymore. This has happened on several occasions !