I didn't really watch, though it was on and I heard a fair amount. The thing is, not watching doesn't make me an uninformed or uninterested voter, which is what this article about the ratings (high but not as % of voters) is implying. In 1980 there were newspapers and local rallies, but for most casual voters the debate (only 1 in 1980) really was the only way to get to understand who the candidates were with respect to each other. That's not really true today. Between cable news, and the internet there is far more exposure for the candidates than there was then, and people who want to know about them already do.
Further, this election paints such a stark contrast that it's actually really hard to not know who you will vote for at this point. I suspect that many to most "undecided" voters are really just in the process of acceptance. They will end up voting for Hillary Clinton or Gary Johnson (or staying home) but aren't happy about either choice.