Many other states do charge sales tax. I think 48 states, in fact. This sales tax is for in state sales.
The recent development is some 29 states now require out of state businesses to collect and remit taxes on shipments to the respective tax-charging states. Another 13 or so have plans in the works to do the same.
In a lot of cases, it's a simple thing and there's often a minimum amount of yearly sales to the respective state that triggers the collection and remittance of taxes. Some states require the tax calculated for the total item and shipping cost. In other cases, there's not a minimum as the greedy-greedy-pig state wants it all.
In a few cases, there's also a facilitator tax collection and remittance requirement. A facilitator is a market like Amazon, eBay, Etsy, etc. that facilitate sales to buyers for a group of sellers. In that case, the facilitator calculates, collects and remits the tax on behalf of the sellers it represents.
The tax charging outfits aren't doing it by choice. The greedy-greedy-pig-fucks force them to under penalty of theft of their business, loss of their livelihood, and death at the hands of the states.
That's probably their explanation.
Some probably don't meet the de minimis sales amount - where it may exist - to require collection and remittance and don't.
Others might actually just be hoping not to get caught or believe it should be incumbent upon the buyer to remit tax where required and don't.
A few are just doing it because they don't know any better, got bad advice, fearful of losing their life, or think that tax is a social necessity and government imperative.
I don't have beef with those people. I just choose not to do business with them. It annoys me that the pigs attempt to invade every aspect my life. It annoys that some of these places use non-standard tax rates or seem to round up the tax calculated. I get the last part; they're just trying to limit their liability but the cynic in me thinks they're just skimming off the top with the tacit approval of state laws.