That's probably the case. They're too big and expensive rights wise to keep releasing single seasons... though for Batman, I wish they did. That third season sucked. 'cept maybe for Eartha Kitt's Catwoman. I mean, the first 2 seasons were tongue in cheek, dancing a line between making it look straight up for kids, and sarcastically snickering for adults. The third season was "let's see how funny we can make this." Actually... here's my "what's the deal?"
Why does anyone actually like Batgirl? I swear, every time she's involved with the outside franchises (don't know much about the comics, I only follow the big groundbreaking stories like "Killing Joke"), the project starts to suck. Okay, maybe Batman TAS is debatable... but look me in the eye and tell me she didn't suck in the fourth Batman movie (the one everyone hates) and when she popped up in The Batman (her debut season was the worst season of that show). I mean, there are those who dislike Batman Forever, but manage to write it off as meh (meh is better than horrible)... but just any time she appears, the franchise gets ruined.
Also... ever tend to notice that once Superman appears, that's when you know a Batman cartoon is on its last season? Batman TAS, The Batman, Brave and the Bold... I mean, obviously they're saving Supes for last season, but it's so incredibly regular, that's how you know it's over. Heck, I wouldn't be surprised if they just threw Superman into the 20th episode of Beware the Batman, since they want to get rid of it so much.