Because those guys were meant for music, not for explosions et al.
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There are very real advantages to using bass management in 2.x systems -- lower THD, lower IMD, increases in dynamic range, potentially smoother bass response -- all due to removing the lower bass from the main speakers and amps and letting the sub(s) handle it. In general, movies tend to have more bass than music, but any system aiming to be high fidelity should employ bass management.
I've used analog bass management controllers in the past, but now rely on digital. As a plus, most AV gear now provide room mode correction as well.
A simple answer to your question regarding analog electronics companies not supporting bass management is that their target market doesn't want it. The same reason applies to active speakers -- they offer many advantages over passive designs, but there is effectively no market for them outside of the pro audio community.