(1) Elasticity-- it's hard for both personal/morale reasons and legal reasons to lay people off, but it's easy to increase or decrease contractor utilization as needed.
(2) Expertise-- sometimes you need someone with some specialized know-how and you only need them for one job.
So if I'm understanding you correctly then the best thing to do on my end is:
1. Look for a niche in which I have a deep level of expertise.
2. Target only those employers. With evidence of this expertise.
3. When targeting those employers, only seek out the ones that tend to hire people on a short term basis. I.e. project-focused company, like an agency or something along those lines.
Is this a good assessment of the heuristics I should be following?