From a tax point of view, EU is a lot easier to deal with than the US if you have to collect sales tax in the US.
There are two big differences.
Let's say I'm selling some digital good online. Consider three purchasers, one in the US in the state of Washington, one in Germany, and one in France.
First, how much tax do I have to collect from each?
For the German customer, that is easy. It is 19% VAT. I don't have to care where in Germany they live.
For the French customer, that is easy. It is 20$ VAT. I don't have to care where in France they live.
For the US customer in Washington...it is not easy. There is a state wide 6.5% sales tax, but there are also county, city, and other sales taxes that I have to collect. For example, if the customer is in the city of Seattle, I'm supposed to collect the 6.5% state tax, plus a 2.7% city tax, plus a 0.4% for something called the "Regional Transit Authority"...that's 9.6%. If that person is over in Bellevue instead of in Seattle, it would have been 10% (6.5% state, 3.5% Bellevue).
For the US customer, I have to care where in their state they live. Also, tax boundaries are not guaranteed to line up with postal code boundaries, so to do that tax accurately I really would need to collect their full postal address (which since I'm selling a digital good I have no use for except for calculating taxes).
Second, what do I do with the tax I collect?
For the EU, I sign up for the VAT MOSS system in a single EU country. Then each quarter I have to file a simple form with the tax authorities in that single EU country that simply lists each EU country, what my total taxable sales were in that country, the VAT rate I used, and the amount of VAT collected. I turn the collected VAT over to that single country's tax authorities. Then they deal with distributing it to all the other countries.
For the US...I have to deal with each state I collect tax for separately. Each has its own forms. Each has its own place to file them. Each has its own place to pay.
If you have to deal with more than just your own state and maybe a handful of others in the US, you pretty much have to use a third party service that specialized in handling all of this. For companies in lines of business that are only barely profitable, this could be prohibitively expensive.
If Congress ever decides to require online companies to collect tax for all states, instead of just those that they have a presence in, and they do not require that the states use something like the VAT MOSS system, and they do not require that each state has a single rate for out-of-state non-present sellers, it's going to be nightmare for small companies, and possibly drive many out of business.