Part of it is the fact we have reasonably competitive races on both sides of the Aisle. In 2012 I don’t think Obama debated anyone (there was one minor candidate debate) and the Republicans were done debating by February 2012. It’s pretty unusual to have this many legitimate contenders still around at this point in the game. Clinton has a lead, but not so much she can say “no more debates” to Sanders.
There were quite a few debates in 2008.
Also, with the Trump Circus and the fact there were something like 17 Republican Candidates originally, I think people in general are just more aware of the debates. They’ve been a ratings bonanza and in turn every news organization wants to get in on them.
