Those clean up guys don't get paid enough. Whatever their salary is, it isn't enough to deal with 2 years worth of adult diapers.
I think she kept them because she was afraid/embarrassed that someone would find out if she put them in her trash.
It's one thing to have a field mouse get inside through a tiny gap or even to have bats/squirrels in the attic, but to have goats and opossums getting in because there is a gaping hole on the side of your house is just unreal.
At the beginning of the show, there's text on the screen that says how many people are hoarders. Can't remember if it says 3 million or 30 million, but even if it's the lesser, that is still a lot of junk being kept in secret.