Just as often, contractors who get money from the regulation. For example, insurance companies who favored Obamacare because they thought they would make money off the insurance mandate.
Another example, a certain online dating website offered a background-check service. They lobbied the government to require that all dating websites have background checks on their users. Fortunately that one didn't pass.
Another example, in California, a company that made portable classrooms lobbied for a requirement that all schools use portable classrooms. Now a bunch of schools across the state are stuck with these eyesores.
The more complex the regulation, the easier it is to hide stuff like that in it.