Because of those wonderful NO STANDING PERMITTED MOVING VEHICLES ONLY signs. Since no one around here seems to have any reading comprehension, people pull up, see the sign, and drive away. They don't actually consider the dates and times on them. This morning I saw a completely vacant stretch of about eight parking spots on a block where parking is usually at a premium. I saw drivers pull up, glance at the sign, and leave. The sign clearly stated that there was to be no parking there. No parking tomorrow. Since it's today, I pulled up and parked there. For a session yesterday, I used a spot that was reserved for this past Saturday and Sunday. I'm loving these parking signs. I hope they stay up for a long time.
[Image shamelessly stolen from http://www.thepermitguy.com. Link also included in the event that I get google hits for people looking for parking permits. I don't provide them; I just think they're awesome. The Permit Guy can get you one though.]