"Consumer" products don't tend to come with "Business" in the title.
Leased lines are no good for pure-download capacity and we have no need of upload capacity (beyond about 3 occasional VPN users, we have no external-facing servers, but 400+ downloading users during the working day). And have you SEEN leased line prices? The words fecking and ridiculous come to mind. We have 48Mbps download, and the equivalent in leased line would cost hundreds of times more than double business-ADSL2+ lines. I quote the top Google ad for UK leased lines: "Leased Line ****FROM**** £299 p/m" (and they barely start at 2Mbps). We pay about £50 a month at the moment.
The problem is not the technology, or the capability, or even the occasional disconnection, it's the service compared to their rivals offering similar products - but I've never seen something ADSL disconnect that often, consumer or not. BT are the most unreliable ADSL2 provider. And 99% of businesses will never be able to afford even the most basic leased line compared to a similar DSL line.
I can literally buy 12 ADSL2+ ***BUSINESS*** lines from different suppliers (or cable lines, or 3G connections) and load balance them for less than the cost of a 2Mbps line. I'd also get 12 phone lines thrown in for that, 288Mbps of download capacity (and, yes, you can load-balance most web access quite easily and effectively, especially with the right caching), 11 redundant lines and one heck of a cabling mess but hell, I'd rather have that than a 2MBps up/down line with leased-line service.
Not every business is made of money, and not every business has the same needs.