What is the reason why drinking gravy and red beans and barley tea makes me thirstier and thirstier?

Because gravy red bean and barley tea has a diuretic effect, which is equivalent to taking diuretics, the symptom of dry thirst will appear after drinking it, and if this symptom occurs it means that you are more sensitive to this tea and it is not recommended to continue drinking it.
The symptoms of dryness and thirst will usually be relieved after discontinuing use and will not cause irreversible damage to the body.