I had the privilege there of working with some insanely dedicated people, smart, hard-working, and good, who were kept on near-permanent contractor status, and then unceremoniously dumped when the legal limits for contract lengths came up.
And these weren't warehouse workers, these were HR folks, recruiters, technicians, and the such - people in positions that are neither seasonal nor temporary.
Beyond the moral/compassion concerns of this, it wreaked havoc with the team to have a good hire on board for most of a year, and suddenly have him/her replaced with someone unknown who needed even more retraining. It also placed a constant load on the people involved, since you're essentially always re-hiring the same position, over and over, with the requisite interviews and costs. Suffice to say it caused a lot of disruption with the team, and I have to question the wisdom of dragging down the productivity of a dozen people to save money on one.
I can't say I know the official (or unofficial) reasoning for this, though of course the usual suspects of paying out benefits comes to mind. Also, certain headcount metrics may exclude contractors, which might be a way for management to look like they're keeping headcount down while still getting the hands they actually need. Either way, it soured my faith in the company some, and with a bunch of other factors led me to depart from the company.