At first that data surprised me (just assumed that I'd see a more predictable curve) but now that I think about it, it's not too big of a surprise when I think about my experience with alcohol and other recreational drugs. Many people abstain (or nearly so) and many others enjoy degrees of moderate use. It's only a smaller percentage that really takes to their drug of choice and runs into likely addiction and habituation issues.
Normally on that chart I'd fall between the 7th and 8th decile depending on the week but there are exceptions. Sometimes I just don't drink for a few weeks because I don't meet friends for a beer or whatever. Then other weeks like the one between Christmas and New Year's Eve I easily push into the 9th decile between a work party one evening, wine with festive family dinners, and going out for drinks until the late hours on NYE.
I don't have easy access to detailed data for my own habits over the course of a year or more so it's tough to estimate where I'd end up after averaging more weeks together.