"Why can't Americans play poker online?"
American anti-gambling laws.
"Why does Amazon have to collect state taxes for states they don't have a physical presence in?"
Because those states count things like affiliate programs and subsidiary companies as a sales tax "nexus". Amazon tends to kill those programs to avoid being taxable. They only collect sales tax in 24 states.
"Google is forced to censor French and German search results. Facebook is forced to follow EU privacy laws."
Yeah, because they have operations in those countries, and can thus be sued there. Also, perhaps, because they might be blocked in the relevant countries, and would rather stay in those markets.
The EU simply cannot make me collect VAT (or do any other crazy thing they think up), because I'm not in the EU. They can ban me or my services or products in their jurisdiction, or make life hard for my customers in their jurisdiction, which may be enough.