It was MY experience that each quarter was a guessing game as to whether or not you were going to have a job that next quarter. Maybe the client would extend you a month or two. Maybe not. And then it felt like the onus was on YOU not the account manager to source other opportunities at the current client for possible extensions.
Maybe they have other client engagements where the commitments are longer than 3months? Maybe some people only want to work for 3months at a time? I don't know. For me, personally, it always felt like a crapshoot.