There really aren't other offerings online for this chemical and I doubt that the suppliers are doing back alley deals with research teams in the US.
Someone in the supply chain knows exactly what this compound is for. They know people are buying it to be consumed. They commissioned a foreign lab to have it produced. They could have found a pharm grade lab to produce it. They didn't, because the margins are high on quasi-illicit substances produced in Chinese labs.
It was a cheap synthesis to get tons of the stuff on the market quickly with a huge margin. It's certainly meant for human use.
Then why does it come in pill form? And why do they only sell it to researchers - including those doing clinical trials?
It is available to researchers as they are able to use it in non-human assays, experiments and studies.
[1] https://www.caymanchem.com/app/template/Product.vm/catalog/1...