The core problem, from an outsiders' perspective, appears to be jurisdictional fragmentation. Amazon, not unreasonably, want to be able to regard the USA as a single market, yet this gives them 50 different sets of legislation and 50 tax codes under which to operate.
However politically unpopular this idea might be (it's certainly not popular in Britain with the EU, which itself started as a common market and legislation / regulation area) the most business friendly idea seems to be centralisation. Remove competency for this sort of issue from the individual states, create common legal frameworks, allow a one-size-fits-all management model rather than having to individually cater for the requirements of Wyoming, Vermont, Alaska, North and South Dakota, Delaware and Montana. Seven jurisdictions, seven legal codes, seven sets of tax law. Yet only one has enough population that it would even qualify for the top ten cities by population and even combined they would only be twenty-second in population ranking. They're not major markets and a legal framework designed like this is unduly expensive.
Way more than 50 different tax codes (Amazon could probably deal with that), many counties and municipalities have their own laws regarding sales tax too.
On top of that how would Amazon identify if I live inside Omaha 7% (state+local) sales tax, or just outside Omaha 5.5% (state only) sales tax? Nothing changed about my address between when I lived in an un-annexed suburb and after I was annexed.
However politically unpopular this idea might be (it's certainly not popular in Britain with the EU, which itself started as a common market and legislation / regulation area) the most business friendly idea seems to be centralisation. Remove competency for this sort of issue from the individual states, create common legal frameworks, allow a one-size-fits-all management model rather than having to individually cater for the requirements of Wyoming, Vermont, Alaska, North and South Dakota, Delaware and Montana. Seven jurisdictions, seven legal codes, seven sets of tax law. Yet only one has enough population that it would even qualify for the top ten cities by population and even combined they would only be twenty-second in population ranking. They're not major markets and a legal framework designed like this is unduly expensive.