because the amplifier that feeds the tweeter and midrange is not burdened with reproducing bass - which takes multiple times the power.
in a single amp configuration as the burden of reproducing low frequencies taxes the amp, the clipping can be heard as strain or glare through the midrange and tweeter. not good and very tiring to listen to.
with a bi amp configuration the midrange and tweeter amp can coast along unstrained and never clip.
also the midrange / tweeter are isolated from the clipping woofer amp.
clipping is usually not audible or objectionable at bass frequencies but it fatigues like no tomorrow at midrange and treble frequencies.
the benefits are definitely not from bi-wiring.
in a single amp configuration as the burden of reproducing low frequencies taxes the amp, the clipping can be heard as strain or glare through the midrange and tweeter. not good and very tiring to listen to.
with a bi amp configuration the midrange and tweeter amp can coast along unstrained and never clip.
also the midrange / tweeter are isolated from the clipping woofer amp.
clipping is usually not audible or objectionable at bass frequencies but it fatigues like no tomorrow at midrange and treble frequencies.
the benefits are definitely not from bi-wiring.