If you watch those old 30's serials, the acting was indeed wooden. The actors had NO idea what the SF stuff they were saying meant. I often think their use of overwrought phrases like "space radio" and such were so the actors at least had SOME idea what they were supposed to be talking about. Star Trek-type technobabble was decades away, and even there I see numerous ST interviews with cast members talking about struggling with dialogue they didn't understand.
Beyond that, the "good" actors were in films. The serials were the TV shows of their day, and just as for decades TV stars have longed to break out to films, so were the serials the mainstay of the less talented.

Since Lucas has always insisted that Star Wars is a modern day SF serial just consolidated into 2 hour blocks instead of 10 min snippets, he made sure that acting, costumes, weapons, all of it, was as close to a 30's aesthetic as he could manage.




The Jedi Master