Why? LLCs are pass-through entities. US residents will get taxed as income, and non-US residents will not have to pay any tax if their income is not effectively connected with a US trade or business (which basically means that employees do not do any of the work within the US).
Different countries have different laws. What might be seen as "pass through" under US law can sometimes be seen as opaque in an EU country, for example. Sometimes the situation or the double taxation treaty (if there is one) offers no clear solution.
Most western countries also have CFC laws you need to be aware of. CFC laws are essentially "see through" taxation laws to combat tax avoidance, looking through certain corporate structures you would use to avoid tax, e.g. by somehow siphoning off money (legally, through IP payments, interest payments, etc) to a zero or low tax entity somewhere.
I've had some tax disputes before and I can tell you: most of these civil servants are unaware of the international context they're operating in. They mainly audit local restaurants, bookstores, etc. Nothing "exotic". Talking to them, before you meet with some people higher up, can literally be a crapshoot. Some countries, for example, might try to tax your US LLC income as dividend income, before applying corporate (or personal income) tax to it again.
This is obviously often incorrect, but given most people set up US entities because they're cheap / etc (or at least some of the people using Atlas do), you should be aware that a dispute with your local tax authority can follow. Because they are the ones losing current and future revenue. Those can have nasty consequences if you don't have the funds available to hire, say, a good tax lawyer.
That said, totally agree Atlas (or setting up a US LLC) can be super valuable. Just make sure your tax situation is looked at, at home.
Most EU jurisdictions have required minimum capital contributions from the founding shareholder(s), e.g. 10-20.000 euro per entity. Then there's a ton of stuff to file (some countries are more bureaucratic than others), in some jurisdictions you need to visit a civil law notary to incorporate, etc.
A lawyer can easily take care of that for you for a reasonable fee, but most bootstrappers won't consider it, given the price.
