Looking at the infographic[0], it appears be down to advantage/privilege. These people would have less capital resources to be able to afford service and, of course, those living in rural areas would have a much higher propensity to not have the utilities offered in their area(1).

(1) - Added to that should be the consideration that the current design of much of the internet infers that it would be futile to attempt to access it over dial-up.

[0] - https://www.pewresearch.org/wp-content/uploads/2019/04/FT_19...