Why do too many ads read like this?
Because education told us so. Starting at home, we tell kids that's there a difference between the language they speak and the way they should write. So, when copywriters sit in front of the screen (does anyone still sit in front of a piece of paper???) we tend to hear the voices of our parents and teachers, instead of listening to our own voice. And bringing this voice to life. Everybody can be a critic. Not everybody can express their real inner voice and put it into a fascinating piece of advertising. Copywriters, that's your damn job.
Don't listen to me. Listen to the master:
"If you're trying to persuade people to do something, or buy something, it seems to me you should use their language, the language they use every day, the language in which they think. We try to write in the vernacular." - David Ogilvy