If they're reliably billing out at $800/hr to full-time utilization and feel they're being cheated in their take-home comp, they should set up shop on their own. They're a consultant, that's what consultants do. There's no easier structure in tech in which to compete with your erstwhile employer than in consulting.
If they can't do that, whatever the reason they can't is the answer to your question.
Everyone is forgetting realization. What can you actually collect from end clients? What "discount rates" do certain companies get? That ~$800 is rack rate and after discounts, write offs/downs, you rarely realize that entire rate. Utilization is also important. If client doesn't allow charging for travel, and your talent is flying around, they aren't going to get high utilization. But when they are working the rate is higher.
If they can't do that, whatever the reason they can't is the answer to your question.