Bass guitar is not the only sound that a home theater will be trying to reproduce

Even if it worked OK for music, what about
the rumble of an explosion? Or the footsteps of T-rex?

A bass guitar amp is designed for one thing -- bass guitar amplification. Subs are designed to reproduce all kinds of low frequency sounds accurately.

I play electric guitar. My Mesa/Boogie amp sounds great -- but I wouldn't think of trying to play music CDs through it.