Well, what does "get" mean? Has purchased? As in nobody wants to pay for faster service? Or can obtain, as in everybody else is too far from the nearest DSLAM?
People within a bowshot of me have access to both Cable and DSL. I can get neither, but at first glance everyone thinks that my "neighborhood" has both. Then they check and "oh no, we don't serve that address, how odd". Which is why I get my internet access from a semi-local WISP which promises 6Mbps and delivers 5.7. Some of their customers get 20 Mbps, which you will note is still no longer broadband. However, those customers are in areas where there is competition for internet access. AT&T has literally the only fiber run into my entire county, so my ISP brings a signal in via repeaters across four mountaintops, the fourth of which being where my CPE is pointed.
I would expect to see the lowest speeds in the most economically depressed areas simply because people have other priorities.
Well for my part, I expect that it's because Pacific Bell, uh I mean Southwestern Bell, uh I mean AT&T has other priorities, and it has nothing to do with the customer base. If you can't remember that far back, Pacific Bell was notorious for splicing copper until well after you couldn't reasonably splice it any more. And back when we had line sharing, they were notorious for stealing any pair without either POTS or a digital circuit on it to give to one of their subscribers, so if you got your access from someone else across their copper you could expect an interruption any time there was inclement weather or not, because either the weather would get into a splice between the CO and your house, or it would get into some other line and they would steal your pair to use to fix it. But it should go without saying that AT&T didn't come into town and replace all that shitty copper, it's still festering there. And so in some places sure, DSL is great, works even farther than expected... and in other places, DSL is hopeless, and Pacific Bell cut their distance limit from an original 17,500 feet to just 14,000 feet and even some of those customers weren't getting anywhere near their advertised bandwidth.
Eventually the DSL ISPs started getting dinged hard for delivering lower-than-promised bandwidth, which made DSL penetration the absolute last priority for telcos. So now you have what we have now, where DSL penetration is piss-poor, and I have to use a craptacular WISP because there's nothing else available to me.