As someone else pointed out - it works like this: Massdrop contacts company to see if they can make a deal in regards to making X product if Y amount can be sold, if there is an agreement then the drop starts. Once the drop starts, if target amount gets sold then the money is collected and sent off to company making X product. Said company begins making X product and upon completion, it all gets sent to the Massdrop distribution hub. From there, Massdrop is responsible for shipping X product out to customers.
So, yes, Sennheiser makes them but as far as they are concerned, they are making them all for a singular customer - Massdrop - and none of what they are making is going anywhere else. Now, international purchases can be bought through Massdrop, of course, but it still has to be shipped from their hub to anywhere else in the world, hence the added taxation, shipping, etc.
So, be mad about it all you want but it isn't Sennheiser screwing over their customers, it is a specialized product made for a singular customer who, in return, has sold off the product all over the world.
Now, if Sennheiser were to be selling the same product in various locations all over the world excluding yours, well, then it would be their fault. Sennheiser just sees it as a guarantee of a huge chunk of money and their products don't have to sit on a shelf unsold.