A brief search turned up one from Sudan. I don't know where to find a comprehensive list. Don't forget to include non-Americans with dual citizenship. Someone "from" a totally unrelated country might still have citizenship in one of the banned countries and would not be allowed in. See Mo Farah as a prominent example.

I imagine the main concern here is uncertainty, though. The original travel ban was introduced with no warning and affected people who already had plans, who already had visas, and even who were already in flight. There's no telling if and when they might do something like that again. That kind of uncertainty tends to discourage people from trying to make plans in the first place.