Title IV-D is a federal law found in the Social Security Act of 1975, and in the sections, it categorically states that every State in the US should have a child support enforcement program. The federal government funds these programs via Social Security.
Every dollar that is collected from a father for child support is also taken from social security and given to the state agency involved in managing child support. The funding goes to state agencies to help run their child support enforcement programs. Funding is determined by how many men they get into the child support machine. The more men they get into it, the more funding they get. Thus, they are incentivized to get as many men into the child support machine as possible.