That's not especially different from the typical LLC/SPE holding structure where individual properties in a large real estate portfolio are not held directly, but rather by a single-purpose entity that holds each property and then is owned by a larger but distinct entity. You don't want an issue in a single company/property to be able to take down your entire holding company. If someone will lend you money without cross-collateralization, why wouldn't you prefer that?
If PE firm A wants to buy company C using an LBO, it could do so by having C borrow money and then A purchase C, or by creating an entity B that borrows money and then purchases C. Whether B or C owns the debt doesn't change anything meaningful for A, and it's pretty clear that you're allowed to form company B (and really hard to imagine how you'd make that illegal without effects that would be worse than current).