I think a lot of exchanges are trying to play safe. The US I think has the largest market when it comes to cryptocurrency, the US is also the one big government that has not categorically made a stance on it. They keep dilly dallying on the topic.
Binance is a business entity, they would not like a government policy to put their business in jeopardy so they have to be proactive in other that decisions by one government does not put them out of business.
China on the other hand has made a stand on what they think about cryptocurrencies, so you see most Chinese owned crypto based businesses setting up business to conform with what the government wants or go off shore to establish their business.
The long and short of the matter is that no business in its' right senses would want to operate illegally or in conflict with the government.
As for US citizens and their exclusion from trading some Altcoin I think there are other exchanges they can move to.
And those altcoins that are only traded on Binance, I guess the Altcoin owners will have to consider if the number of US people holding the coin are large enough to cause them to get into more exchanges.
Those are my 2 cents thought. Cheers
Thumbs upto the big boss man @crypto.piotr for bringing me to the knowledge of this post.