Appeal to Antiquity is the line of thinking that an idea old being old, means that it is better. The fact that something has been done for a long time is treated as evidence. This argument is usually fueled by stubbornness, and a lack of historical context. It avoids evaluating a topic for it’s actual merits or disadvantages.
Ayurvedic medicine has been used for thousands of years, therefore it must have some medicinal value.