Look at the short-run loss-minimization problem.

In the short run, a business (or an individual) will continue to operate (or work) so long as at least a portion of its fixed costs are covered (that is: you're meeting the marginal cost of operation / labor).

By putting the subsidy of BI underneath an individual, you're covering that much more of their fixed costs, and it may well be that the person is ahead by working at a below-full-cost wage. And if the BI covers enough of those fixed costs, this can be sustained indefinitely.

Again: this represents a net subsidy of the business which is receiving this labor. There's a reason I'm saying BI and MW are complimentary. They address different market failures.