It's probably predominantly because of the switch to mobile computing / smartphones / web being dominant, and everyone referring to programs there as "apps" / applications.

i.e. If you write a mobile app with a function-as-a-service backend, you will never compile what someone would refer to as a "program", so calling yourself a "programmer" (as-in, someone who makes programs) feels inaccurate and a not helpful description for people. "Coder" (as-in, someone who writes code) is a vaguer in terms of the type of code you write and more accurate in terms of what you spend your time producing.