Plus I think another thing is the timing of the series. In the last 30 years we've had 5 different Superman-related series. There was the Superboy from 1988-1992, Lois & Clark: The New Adventures of Superman from 1993 to 1997, Smallville from 2001 to 2011, and now Supergirl, not to mention the Superman Returns, Man Of Steel, Superman vs. Batman & Justice League, plus over 30 animated TV series and Movies, the market has been over-saturated with Superman TV shows and movies, whereas, before 1988, we had had the 2 Superman serials in the 40's and the Fleischer/Famous Studios cartoons, the radio show, the 1951-1958 George Reeves TV series, and 2 animated TV series in the 60's and 70's/80's (the various Super Friends I'm just counting as one series). I think before there was time for people to rewatch those other series, whereas now it's kind of like "Okay, we're done here. NEXT SUPERMAN SERIES is...".
On the other hand, Batman has been far more dominant than Superman in the past three decades. Of the TV series you mention, only one was actually a straight-up Superman series, and we only had one Superman movie between 1987 and 2013. We've also had only one solo Superman animated TV series in the past 30 years (though he's been a character in several team series), plus four solo animated DVD movies. Whereas the past 30 years have seen seven solo Batman films and four solo Batman animated series (five counting Batman Beyond) plus nearly 20 solo Batman animated movies, not counting team-up movies. If anything, I'm glad to see the pendulum swinging back toward Superman lately. He's got a lot of catching up to do.