The growing influence of the internet
The internet as we know it was not yet in full flower in 1992. The World Wide Web had been made available to the public a year earlier, but outside of military and university researchers, the online experience was typified by online services like Prodigy, America Online and the WELL. Still, a few million households had computers and some kind of modem, which was a few million more households than in the previous election.
This, in addition to the growing influence of cable news (the "24-hour News Cycle"), made engagement in political activity a lot easier for a lot more people. In addition to the usual cycle of rallies and canvassing, citizens had the ability to research, discuss and promote their candidates from the comfort and safety of their own homes.
Another factor was great dissatisfaction among conservative voters with the incumbent, George H.W. Bush. The man who ran on a platform of "Read my lips: No new taxes" introduced new taxes. People who would ordinarily forget to vote, remembered to that year.