My take, after seeing why some bikes seem abandoned, but arent....

Many people that can't afford anything but a bike to ride, often leave their bukes locked up outside...and they might work odd hours as well, which when combined with how many folks who are poor tend to not maintain their bikes to the extent we do, can lead to the impression that a bike is "abandoned".

...if it's in or next to a dumpster and unlocked....it's up to you, otherwise it's best to leave it be.