The backpack is one of the biggest mysteries in this sad case, but not as mysterious as some may think. We discussed this back at the time it was found, but I'll repeat it for those new to the case.
Toronto consists of many immigrants with limited English. As a general rule, and especially the working classes, they do not follow English-speaking news. They don't understand it well, they generally work hard, come home, eat, do their chores, and go to sleep. Rinse and repeat. If they follow the news at all, it's more likely to be that from their home countries in their native languages. Again, I'm referring to those who are relatively new to Canada and have a tenuous grasp of the language.
It is totally conceivable to me that there were many, many Torontonians (even those who
do speak English) who were unfamiliar with Mariam's disappearance. This was confirmed when I was handing out flyers about her at the rally on Dundas Square. I can safely say that the majority of people I approached did not recognize her picture or knew anything about it. This is called apathy. Here at Websleuths, we are all interested and informed about these situations. This isn't the case for everyone and it's easy to forget that.
Another theory is that the backpack was originally found by kids. Kids, especially younger than late teens, also don't follow the news much. I can totally see a 13 year-old rooting through the backpack looking for money or an iPod, and then discarding it. I do not see him/her going home to tell mom about it. Nor would they likely be interested in any names in books - just valuables.
Below is a link to three videos shown at the time of the discovery. There is an interview with a man, A.N., (also relatively new to Canada) who found the bag
two weeks before LE got hold of it. He kept it in his apartment for a while, moved it around, and put it under his balcony where it wouldn't get wet. We don't really know how long he actually had it in his possession. We do know that if he saw Mariam's name in the books, he didn't recognize it or report it for at least two weeks.
In the third video, Sgt. Dan Nealon explains that the backpack was found under trees that sheltered it from the rain. He also says it looks more worn in person than in the picture. I imagine that LE probably vacuumed it for evidence and their handling of it got rid of much dust and debris.
http://toronto.ctv.ca/servlet/an/lo..._backpack_091009/20091009/?hub=TorontoNewHome
(My theories and opinions only!)