Can you explain why this is ?
What is it about lower frequencies that compromises passive crossovers?
The problem is that the values of the components become huge. As low crossover points are in three way speakers, then the electonic order is also higher, to protect the fragile mid and keep a large woofer well out of break up range.
Even at 400 to 500 Hz compnent values are high. This means that to make a good passive unit very expensive inducors have to be used, and they usally are not. The compnents alone for my my passive speakers downstairs cost over $400. Only high end speakers like B & W can afford that sort of cost. Even so in their current flagship they raised the lower crossover to 500 Hz. The problems of passive crossovers at low crossover point are wasting half or more of the amp power, core stauration, hysteresis distortion, and even with high cost inductors, excessive DC resistance altering Q, and tuning freqeuncy.
Finally, you end up with horrible amp loads, and make the speaker sound different with different amps. It is these desiigns that have the worst impedance curves and phase angles. And finally if the impedance dips below the DC resistance of the woofer or woofers, then the crossover is in resonance, and you have a lousy speaker. This occurs in quite a few very high priced speakers, I suspect, and you can surmise it from the impedance/phase curves.
Making the speaker a decent drive for tha amp usually involves adding extra high cost components to improve the situation in terms of amp load.
These days an active design is the better and cheaper solution by far.