The animators had to figure out a lot of stuff that hadn't been done before when they were animating the Transformers in the first film, and I recall the writers admitting that the robots couldn't have a lot of screen time because of that, hence the useless human storylines, especially the hackers'. By extension, if animation really was that tricky, that might explain the often-used "shaky-cam" that made the fights hard to watch but hid any potentially sloppy animation sequences.
Now they promise that they know what they're doing, and they have around forty robots. They even pointed out they could even add more robot-only scenes, even entirely in post-production, especially for the Decepticons (who were particularly lacking in the first one).
Forty Transformers sounds like a lot, but it's only about three times as many as in the first film, and it almost seems like they could've almost had three times more screen time than they did. Though I expect a lot of minor characters will end up being background cannon fodder (like Jazz practically was, sadly) - though these background guys will probably help sell toys if they at least look cool in however many seconds they appear in.
