Well its pretty simple.
1. High enough bp you can get majority of his frags through UT(Ultimate Training)
2. He's in chase missions(very rare but it happens)
3. They aren't going to make it reasonable price wise, simply because not everyone should be running around with Tendo.

Hashi is becoming cheaper and cheaper simply because he's only obtainable through RNGgodmode luck from boxes. Way more people have Hashi than tendo as well. There are only 3 in my server who have tendo and me being one of them. And we have whales in my server. They eventually give the rest of Tendo to everyone but that's probably way down the road after they milk him. Lastly, people sleep on tendo's effectiveness. Myst isn't a prompt but 57% mood and he's almost 1 shotting people around the same bp. Not many ninjas can do that Aoe wise. Acupuncture on chase is way better than the interrupt on hashi's. He still gets the job done for the most part.