The Australian federal government goes through waves of "reducing the size of the public service" by firing and/or capping full-time hires, but the work's still there to be done so contractors get the gig.
This is the thing. Its much less expensive to have these sorts of knowledge employees on government staff who just do this sort of work all the time, but governments prefer to spend more (much much more) on contractors. I suspect its partly because they are always wanting to announce down-sizing initiatives to appease the right, but I think more cynically, its because contractors will more reliably give them the 'right answer' than career civil servants and there's also the potential for kickbacks. Some of those profits paid to contractor companies might find their way back into campaign contributions.