Online betting was huge in several other developed countries first. America got late to a trend. If anything, a Great Firewall in the USA would have protected it from the trend.

America banned international countries from winning the betting market to protect Vegas and casinos in general. Some sort of protectionism they said the war on Terror was the reason to ban it if I remember correctly(just after 9/11).

America was much better on betting a few years ago, it's been very recent.

I would have thought that trump giving so much to christians, he would be against betting but there are things that are beyond my understanding.

Trump is great at gettinf christians to completelt forget their moral stances

Gambling is extremely popular in china despite the firewall and laws around it.

Does China have online gambling banned? I don't know

Yes all forms of gambling, except certain government sanctioned lotteries, are illegal and criminally prosecuted

Except in Macau, where casinos remain permitted. Chinese can also cross to Cambodia, where Chinese casino tourism is probably the bulk of the country’s economy.