Likewise, there are plenty of non-business flights booked last-minute like that, too - like, as a personal example, needing to book a same-night flight to help a family member drive cross-country with her kids and personal belongings so she could get out of a dangerous personal situation.
All this being to say: if price differentiation between in-advance v. last-minute bookings is actually intended to make business travel cost more than leisure travel, I'm thoroughly skeptical of that intent being fulfilled in practice. Seems more likely that it's simply a matter of things costing more when they're more scarce (as seats on an airplane would become as it gets closer and closer to the departure time), and that just so happens to impact business travelers more than leisure travelers.