I grew up with “pop” being the word for a fizzy beverage. Maybe “soda pop”, but it sure as heck wasn’t “soda”. Then I went to college in the middle of “soda” country and was derided for my hillbilly term. It became part of my style, and to this day, people are surprised when I bring over a two-liter and declare that the pop has arrived.
The distinction between the two terms (as well as “coke” as a generic term for pop) is largely geographic. A large-scale internet survey constructed a map of the preferred term across the U.S., with pop dominating the Midwest and Northwest, soda dominating the Northeast, Milwaukee, St Louis, and the Southwest, and coke gobbling up the South. SeeTweet develops a simplified version of this map with little effort.