Amateur equipment can be ordered through amazon.com but a check of the TS-590 and the FT-859D shows HRO to be much less expensive.
the key word is "through." Amazon is not the seller in these cases but allows third party sellers to use the Amazon website to sell items. Sometimes Amazon is not the seller and in addition to letting the seller use their website, Amazon also ships the items to the customer (aka: Fulfilled by Amazon). Amazon decided to compete with eBay and thus a percentage of what you find on the Amazon site is not stuff sold by Amazon directly. In general Amazon sells its stuff at GREAT prices. Amazon third party seller prices are often not so great (as is the case with the Yaesu items you reference). HRO or AES (or Yaesu, Icom or Ten-Tec) could decide to become Amazon third party sellers and that might make the prices better...
When you are on an Amazon page, look to see if the details say "ships and sold by Amazon" or "sold by X and Fulfilled By Amazon" or "Available from these sellers." The stuff which says ships and sold by Amazon is the stuff in which you are dealing with Amazon as the seller.
It wasn't ham radio related, but I recently made a purchase online and it was shipped via FedEx who dropped it off at the local post office who completed the delivery. I found out this is becoming more and more common. At least it fit in my mail box.