> When did the US develop this entrenched gambling problem?

In the 2010s the TV networks normalized fantasy sports into sports betting. The vehicle they used for this was through the 45 second commercial advertising breaks that run every 2 minutes during American football games, and then across the other important American sports thereafter. If you were a regular watcher of sports in the US you've been brainwashed over the last 10 years into thinking this is ok. Some are aware of this, many are not.