I have a lot of other things I can be doing beyond watching movies, like playing video games, online games, reading books, or even having sex. Waiting a month (when it has already been how long since it has been in theaters?) is no huge feat.
Of course they're trying to cripple rentals too, again in an effort to increase sales.
If I'm spending nearly 5$ to rent a movie, it's very unlikely I'll touch that movie as a purchase for 20$ just to see the 10 to 20 minutes of blooper reel.