I notice among people I talk to more enthusiasm toward learning French than Spanish. This confuses me; my feeling is that Spanish unlocks far more countries and speakers than French does and so is a more natural first choice.

What do people think motivates this choice?

Maybe because among those in your circle learning a language is less about its function and more about some aspirational quality. In spanish-speaking world learning English is definitely more about its function. Unlocking access to global content, jobs, etc