Trust me, I really wish it were that easy. We're based out of Spain, so to sell in the US (or other countries) we either need to figure out assembly of the device there, or we need to solve cross-border payments, logistics, customs clearance, tax remittance to individual states, and hardware compliance. That said, we're working hard on all of it and plan to go D2C as soon as possible.
I haven't used them myself, but it seems that services such as paddle.com takes care of the payment and tax compliance. There are probably similar sevices for logistics as well.
The thing is majority platforms like paddle.com don't supoort hardware products. I was looking at fastspring as well but hit the same wall. I will still try reaching out to paddle.com support to see if they will allow it. Thank you for the suggestion.