Well I will say that's not just the prequels. That's sadly the style right now which is why Hollywood is in big trouble.
Only with bad directors. That was the main problem of the completely screwed up Last Airbender movie. For someone who claimed their a fan, they forgot the show had moments of lightness to it. Everyone in the film acts like someone just died in front of their eyes for 90 minutes. The film was basically a Harmony Gold dub of the cartoon series. Harmony Gold, you see, would shove entire anime series into 80 minute DTV movies and link everything together with tedious long narration to connect all the plot holes that cutting a TV series to 90 minutes causes. And it wouldn't have been so bad if M. Night Shabbadoo gave the film to someone who knew how to direct an action film... or someone who knew how to direct period.
Serious acting doesn't call for wooden directing. There are some parts of the original movie that seem to run the gamut from wooden to hammy, but they found a balance as the series progressed. But even when it was like that, it wasn't quite as obvious. The movies still had an amount of fun to them, and that could be overlooked. Long tedious bits of plot expo, wooden acting and cheesy lines stick out.