In Bao Shan's view, a sect like Azure Dragon Temple is unlikely to have anyone specializing in the Poison Dao.
Because it's not worth the trouble.
The Poison Dao is easy to learn but hard to master, and it consumes a lot of time.
Meanwhile, practicing the Martial Dao is like a race against time, where one cannot afford any slackness.
If one cannot achieve something before the age of forty, there's no hope for a breakthrough for the rest of their life.
This means the time left for a person to cultivate is incredibly short, and any slight negligence might cause them to miss their chance, leading to all their previous efforts going to waste.
Not to mention others, Bao Shan himself is an example.
Due to delving into the Insect Poison Technique, he was ultimately too late to breakthrough to the Fifth Realm, and his martial potential was thus exhausted, leaving him with no chance to open his meridians.
