In the USA licenses are not contingent upon manual vs. automatic. No one checks what car you drive. So you would have to learn somewhere - someone around you has to own a manual car in order for you to learn how to drive one, and here simply no one does. No one in my entire extended family, none of my friends, none of my coworkers I'm friendly with, none of the 50+ cars I have any tangential access to are manual. So even if I wanted to learn, what are my options? Buy an entire car just to learn? Services like Turo won't let you rent one unless you can drive one already.

We have Driver's Education in high school but it involves no actual driving - there are separate paid/private courses you can take that might involve defensive driving or learning stick. I did one on controlling skids on wet or snowy pavement and demonstrating e.g. turning under braking with and without ABS. But nothing about manual.