Some countries have variance in what is considered OTC. Mexico for example will sell you metoclopramide at a local drug store, while here in the United States you'll need a prescription for them. India and China have become large producers in legal medication, so it's not really rocket science why someone wouldn't sell legal medication from ndia onto the clearnet. These services are not illegal. They may operate under a grey area yet there is no one actively doing anything about them. Many actual people utilize online pharmacies (e.g. Indian ones) to get cheaper medication without using insurance or visiting a doctor.
This is the easy way to get it without having to talk to any doctor that is able to write a script. There are online doctors you can talk with, have your insurance charge it, and you take it to a pharmacy to have filled. Some social engineering is necessary to get what you want. Some may hassle you into using another medication than what you actually want. This route is quicker while also being a little bit difficult for some.