How are other exchanges still operating in the US and Binance sees no other way than blocking?
Remember that they are the liars who said everything was perfectly ok, denying rumors while making their suitcases and fleeing Japan because they couldn't meet the regulations. And of course, others could.
They are currently residing in Malta, the most lawless and less regulated country in the EU, when the government will start looking into their business they will probably head for the Bahamas.
I haven't read CZ's official statement regarding this but as I have seen on their Terms of Service, they cannot serve/cater to customers who are residing in the US and is covered by UN Security Council sanction list:
By accessing and using the Services, you represent and warrant that you are not on any trade or economic sanctions lists, such as the UN Security Council Sanctions list, designated as a “Specially Designated National” by OFAC (Office of Foreign Assets Control of the U.S. Treasury Department) or placed on the U.S. Commerce Department’s “Denied Persons List”. Binance is unable to provide services to any U.S. person. Binance maintains the right to select its markets and jurisdictions to operate and may restrict or deny the Services in certain countries at its discretion.
Sure Binance operates on an essentially lawless state for crypto but how about those who they are serving and those using their platforms? No other choice but to block US residents for the mean time and just create the region's own exchange than to incur a lot of penalties and being issued a cease and desist order if someone gets caught doing something fishy on their trading platforms.