The reasons for this are as follows:
In a city that claims it has a very green consciousness, it's ridiculous to see someone create trash they will never clean up, but will instead fall away into the streets and blow into pea patches where someone else will clean it up.
Printing with an inkjet produces a copy that will smear and run and deteriorate like nobody's business when the rain comes down from the sky. Which it frequently does in this city. Cheap sheet protectors only protect from light condensation for something like two minutes, which doesn't do a damn diddley squat in a town where it rains for 72 hours straight at times.
If it is so important for you to advertise your lost animal or yard sale, then why do use something that is so vulnerable to the elements. If the message is lost, the content is gone, and you've failed to achieve anything.
Take a lesson from most of the pros, i.e., those people who tack upcoming shows to powerlines and busstops. Use a laser printer, and if you must sheath it in some sort of protective material, use a 5 mil or higher laminate. Even without the laminate, you will notice that a laser printed poster will last at least six months, and not the two days that an inkjet might survive for.
It annoys the hell out of me.