Given your answer, why then don't the VND market makers at those exchanges create liquidity at Bisq exchange?
It is decentralized and non-custodial, and has been available for years.
I don't trade on Bisq (actually I heard of it) and after reading your post, I visit the website and found that Bisq is for app trading only (please correct me if I am wrong at this point). Bisq will be great if people can trade it directly on web brower, and if Tor is allowed it will be more convenient for guys who take care of privacy.
Personally, I don't like to trade on an exchange that does not provide trading on web browser. In the past, I used to trade on Crypto Bridge exchange which is a cool one but eventually their team did an awful scam exit.
Trading through a web browser means using a web server, which would centralize Bisq in that server.
So, that would defeat the purposes why Bisq was created.
However, what you mean already exists at:
https://hodlhodl.com/Why do you think the VND market makers avoid creating liquidity there also?