Inferences you can make about users leveraging footer navigation vs main nav?

I am using FullStory to study some user behavior on some client sites and have noticed a trend in a few client sites where users will opt to use the links in the footer navigation over the main menu.

My initial reaction would be to assert they are doing so because they feel it has a lower interaction cost than the main menu or because the footer nav is simpler.

It could also be that after scrolling to the bottom of the page it seems like a lower friction action to use the bottom navigation.

Unfortunately I can't ask these users who exhibit the patterned behavior, so instead, I wanted to reach out here to see what other UX professionals might have to say on the matter.