most large companies have a 2-year limit on contractor employment so what they tend to do is they'll hire the same guy through a different contractor with another two-year agreement..... that's to get around the situation where if someone is working as a contractor for more than 2 years they can legally claim that they're actually an employee....see Vizcaino v. Microsoft Corp., 120 F.3d 1006 (9th Cir. 1997) [0]...

this is just a guess by the way but it seems like a plausible one, as I've seen it happen in Fortune 500 a lot, where the same guy comes back through a different vendor 2 years later if he was really good and they needed him to come back....

[0] https://law.justia.com/cases/federal/appellate-courts/F3/120...