For me, it's pretty simple, really.
When you're new to flying, everything is fresh and interesting, and the majority of us become sponges and soak up everything we can - and that includes the fora experience. You learn to put up with the blowhards, the sky gods, the fantasists (whatever did happen to dear old DSC?), the arguments, the willy-waving, the plain stupid, and the "good ol'boys" who have evidently flown everything ever made since the Wright Bros strutted their stuff, because there are a lot of good guys who are willing, unfailingly and selfishly, to help you along with many of the confusing aspects of this game.
Over the next few years, many of us try to do our part in turn to help out. And then ....
A few more years down the line, with some/a lot of (delete as required) experience under the belt, it becomes much harder to find the motivation to continuously monitor and engage in discussions, many of which - let's be honest - we have often seen before. And as a result, the habit of logging on to see what's going on starts to slip away, to the point where - in my own (and shameless) case - these days I only log on if I need to ask or research something, or if I'm sat idly bored in front of t'Interweb.
As that irritating puppet is fond of saying, "Seeemples !"