I think it really comes down to the proximity to areas that speak that language. I can travel 100s of miles in every direction from my home in the US and only find English speakers. If there was a town that spoke Spanish 50 miles away, I may consider picking it up. Not many Europeans speak Chinese, why do you think that is?
A coding challenge for someone with more GIS knowledge than I have: use the dataset behind this map https://hub.arcgis.com/maps/847cabe2dfc64f92918f2c282e3cedfb (number of households where Spanish is the primary spoken language by census tract) and see if you can find a location in the United States where you can travel 100s of miles in any direction without encountering a Spanish speaker.
Yup, why should I learn it? I simply have too few occasions to interact with someone who speaks Spanish but not English that it would have been quite a waste of effort to learn.
As an adult it's really hard to pick up a language to be conversational. I tried, it's alot of dedication.
Then I went to Mexico, no one understood me. I guess I have an accent or issues with pronunciation. If I did ask a question, I didn't understand the answer. Everyone just spoke English.