Because they are grandfathered in; if they go edit their sig, they will find that the images have been erased and can't be had back. When theymos decided to ban sig images, he didn't want to go erase all existing images, so they just get erased when the sig gets changed.
I don't disagree that it is good to discourage the use of very large, and multiple, images like in that example. Isn't it possible, with this forum software, to restrict the image size in signatures to something small and unobtrusive like those 19px high userbars?
But anyway, don't people on forums like this ever frequent other forums where you see those kinds of userbars (I have seen them on gamer sites and sites related to movies, tv, and popular culture... e.g. anime)? It just seemed to me to be a better way of subtly spreading the word about bitcoin. Rather than an in-your-face marketing approach intended to actively influence others ideas and behaviors, which so often annoys, it is more about personal expression, "These are some of my favorite things".
Rather than turning others off it may possibly leave space for curiosity and open-mindedness to arise. Rather than making people feel like they are being told to do something (even a rather innocuous phrase like "ask me about bitcoin" is still a command
), it may allow them to approach it themselves, as something they have chosen to do on their own.
"Bitcoin? What is that I wonder? Some kind of money? I like money... let me investigate."
Unlike some I don't consider the vast majority of the population to be sheep, even on those type of sites I mentioned, it just seems like that with the poor signal-to-noise ratio, and it is those non-bleaters with minds of their own that it would be good to have join us.