In most buildings, that's how it is if you want to create FT jobs. There are no back to back sorts.
Hell, most building only have 2 sorts. The preload in the morning and the reload, or local, in the evening. How do you get a FT job out of that unless you have 8 hours between shifts?
Some hubs it can be done. There are back to back sorts or an hour between sorts. It might just depend on how bad someone wants that FT pay and benny's that come with it.
Work PT, make $25K a year and have to work another job anyway to raise a family. Do a split shift, or a few hours between shifts, make $75K per year and don't have to work another job, plus the FT retirement.