Your post is weird. Why would the amount of visitors to a country have anything to do with passports issued? The U.S. is less than 5% of the world's population. That's a hard limit on the amount of passports that can be issued.
The amount of visitors would be limited by the size of the tourism industry and regulations around entry visas. This is an unrelated metric.
That doesn’t mean it’s easier to enter the US than to leave. The US is a desirable place to live, so not many people leave while lots of people want to come here.
It is in fact, 4x easier to enter the US than to leave. Passports are actually rare for a US citizen to have, you just live in a bubble.
[1]: https://www.trade.gov/sites/default/files/2021-03/Fact%20She... [2]: https://travel.state.gov/content/travel/en/about-us/reports-...