Porn is very different.
Most guys, even married ones, have a constant need to jerk off, and they like seeing new material to do it to.
So just because you downloaded porn last month, that doesn't mean you're set for life.
It is my assertion that AshleyMadison worked for a VERY SMALL percentage of its users, with the rest running into frustration and epic failure. While a guy might keep renewing his membership for a few months if their bots keep stringing him along, eventually he is going to declare the whole thing a bust and move on.
I don't think there were many members who kept paying for years without having a single affair. Perhaps there were a few gullible idiots who did so, but I doubt all that many.
Most scams rely on a constant stream of new victims, rather than attempting to milk the same ones for years.