I will give people the benefit of the doubt and assume that voting simply isn't convenient or accessible to them.
Offer voting by phone, website, or app, and then see what the numbers look like.
I'm Canadian, and the last time I voted it was at a place that you basically needed to drive to. And take time off work to get to. Super inconvenient, despite my motivating to vote being high.
If it were an option by phone or website, I'm sure far more people would, because they don't have to disrupt their lives for something that takes 5 seconds to do.