Again, the simplest shampoo is made easily. No one is saying to start producing paste or any complicated medicines. But he can use what our world provides - a lot of ready-made tools.
Sure you can
make simple products, but only on a small scale. A few hundred units a month would be about the limit before you would hit hard bottle necks in sourcing materials, containers, and overall production capacity.
And that doesn't even take the logistics to move it all to a central location for processing nor bandits/monsters attacking your caravans and competition sending in spies and luring away your workforce.
Why bother worrying about setting up, staffing, maintaining, and protecting multiple buildings, refineries and transportation hubs, when he can just order a few pallets to a warehouse he builds near the cabin and brings products over as needed.
In this way it simplifies logistics as he only need to move and protect the finished product, and completely removes the competitions ability to steal any carried products production method. Not only that the product remains consistent and the only bottleneck he will encounter is otherworldly shipping to the cabin, and the fact he has to move products thrue the portal himself.
Yes that last bit is something of a major speed bump,
but, and its a big one, that is nothing compared to building three or four major industries from the ground up just to mass produce something as simple as soap, shampoo, and conditioner.
----edit----
Importing the tools would only be a half mesure. Anything that requires electricity would take a tinker/mechanical engineer to convert a local power source to make it work, which is no small feat in of itself. And no, bringing over portable generators wouldn't work. Protecting a solar farm from monsters would be a nightmare, and fuel based generators would take as much effort to fuel as just transporting the finished products.
One final thought is that unless the MC plans to flood the entire world with his products, there is no real reason to build and maintain production facilities in this world. It would also devalue his own products. So anything more then a couple pallets worth of any one product a month is wasteful.