What non-obvious culprits could cause an MPG drop in my 2015 compact SUV?

[RobertVT]

I drive a 2015 compact SUV for a long highway commute, and my fuel economy has dropped noticeably over the past few months, from around 32 MPG to barely 28 MPG on the same route. I've kept up with regular maintenance like air filter changes and tire pressure checks. For others who've tackled similar drops, what are the less obvious culprits I should investigate, like fuel injectors, oxygen sensors, or even driving habits, before assuming it's a major mechanical issue?