Dialup is just too slow. Most light (or even average) internet users might not use much data, but when they DO use it, they want it fast.
This includes people like me. I don't use much data per month compared to most Slashdotters (typically under 20 GB), but I do want to download something, I want it fast. I don't care that the amount I can get each month is limited, but it would piss me off having to wait an hour to download a music track, or 40 seconds to load a basic webpage (like on dialup).
I live in Australia where most ISPs sell a variety of plans with different download limits (from tiny, just a few GB, to massive multi-TB caps). ADSL/VDSL plans are 'tiered' by their download limits, not by their speed as they are in the US (here, you simply get the maximum speed your phone line can manage - this will be faster the shorter your phone line is, up to the 24 Mbps maximum for the ADSL2+ standard, or up to the 60 Mbps maximum my local VDSL2 provider gives).
So I buy myself a 30 GB/month plan and that fits my needs. In the US, for the same cost, I could get an unlimited plan ... BUT it's artificially speed-capped (since in the US the plans are differentiated by speed and thus are artificially limited to a certain speed depending on your plan, e.g. 3 Mbps/6 Mbps/12 Mbps etc.) For me, I much prefer my 'limited downloads @ uncapped speed' than the 'unlimited downloads @ much slower speed' I'd get for the same money in the US. I always have the option of upgrading to a higher cap if I need it ... but in the meantime at least I can grab the files that I do need very quickly.
I actually tried a dialup connection a few months ago as a bit of a laugh. First time I'd used a dialup connection in over a decade. It was way more painful than I remember - web pages are so much more bloated than they used to be. Dialup is essentially unusable now for ANY purpose other than text-only email so I don't think it's a valid option even for light internet users.