You may think there is unreasonableness here, but is that unreasonableness Amazon's?
For Amazon to enter online sales of weapons, they have to address a mess of state and local compliance issues which are not their core competency. No matter what your opinion is on firearms and ammunition, Amazon's reticence as a business to get involved with that seems very reasonable to me.
Not really -- Amazon would just have to have a policy along the lines of, "We only sell guns via gun stores in your local area," and their legal team would only have to ensure compliance with regulations in 50 states (and whatever other countries they do business in). The last rifle I purchased was from a friend in New York, and he mailed the rifle and the case to a local gun store, which is basically what the law requires. Amazon could do the same in the USA if they were willing to enter that market or were willing to allow third parties to use Amazon for such transactions; I suspect that their corporate image is a bigger issue than the law.
A big part of Amazon's branding is that they sell online, and ship direct to you. Doing as you suggest would involve special messaging and a custom workflow to select the local gun store that they are willing to ship the gun to. Also custom workflow for potential problems and complaints (including a mapping ability to locate those stores, and resolution mechanism if the store chosen turns out to not be there, not willing to participate, etc.)
Not impossible, to be sure. But it sounds like a lot of work and potential customer problems.
Amazon would just have to have a policy along the lines of, "We only sell guns via gun stores in your local area,"
Federal law already requires that anyone selling guns by mail-order do exactly that. A gun can only be shipped to a licensed dealer, who must then perform a background check on the buyer before handing it over. It's common enough that almost all gun stores have a set fee for providing this service.
Amazon doesn't do alcohol, either, which could also be for "corporate image" reasons, but does also have compliance issues (federally but mostly state-by-state).
It could also just be an economic decision, but given that Amazon prohibits certain firearms parts which aren't regulated anywhere (except maybe APO mailing to military, or internationally) like trigger assemblies, it seems more likely a corporate image thing.
For Amazon to enter online sales of weapons, they have to address a mess of state and local compliance issues which are not their core competency. No matter what your opinion is on firearms and ammunition, Amazon's reticence as a business to get involved with that seems very reasonable to me.