Businesses are rational. If they need what you're selling, and buying it from you is more cost-effective (inclusive of risk) than building up an internal process to deliver it themselves, they'll buy it.
This apart from the fact that transforming an employee to a contractor is often a net financial win for a company. Not just because of benefits, but also because when the contractor finishes, you don't have to find a way to fire them.
Another thing that contractors are good for is mopping up the unspent money allocated to various line items. Most places with a union/enterprise bargain contract don't allow the employer to a project without a full time equivalent wage attached somewhere in the budget. So when there's a few thousand left, it might be difficult to spend.
Enter, stage right, the contractor, to whom no such rules apply.
This apart from the fact that transforming an employee to a contractor is often a net financial win for a company. Not just because of benefits, but also because when the contractor finishes, you don't have to find a way to fire them.