This is largely because some of the packages they give Flex drivers are downright nasty smelling, and as a result they have to use Febreze or the likes to deal with it.
Could’ve gotten wet in transit, in a station, their contents (I had a package that was wet cat food that was on top of everything else at the station, it leaked..). A ton of reasons. I did preload at UPS two years ago during peak season, station sorting can do crazy things to packages heh.