I'm totally theorizing here, but I have a feeling the producers and creative team think they can create the illusion that Betty is currently widely known and loved. The show as presented, makes that assumption.
The combination of a very compelling leading lady and energizing the target audience (tweens, girls nights out, etc..) through social media, could very well make the show popular with those audiences.
Parts of the the audience ate up Betty's power ballads with thunderous applause and the dreaded "woo hoos."
My section of the audience didn't even clap for some numbers.
Although all the performers deserved applause, it was hard to applaud yet another number (there are many) that did nothing to advance the story and just sort of took up space.