Dunno. Haven't seen any explanation thus far which has made much sense.
Though some time back when I started tinkering with solid state single-ended amplifers which often use a large electrolytic output coupling cap or caps to block the DC offset of the amp, I saw that bi-wiring could afford the opportunity to bypass the main output coupling cap(s) and drive the high-pass section directly from the amp's output.
That's about the only scenario that's made any sense to me at least from a technical perspective.
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