That’s often a misunderstanding. From the content side (movie or game soundtrack) every speaker can contain bass down to 20Hz. And the LFE is an extra channel, not carrying or covering all the bass. If you have a crossover frequency higher up like 80Hz, the subwoofer has to carry all the bass of the LFE channel and all the bass from all the other channels on top of it. That often creates a performance overload for the subwoofer. On thing is that performance overload, another is these church like frequency responses of some subwoofers. That doesn’t help either. They are not really performing as they should with the bass they get redirected from the other channels. At the same time it’s important not to ‘undersize’ the front and surround speakers. Make them as wideband as you can afford to ensure a very good integration. That’s one reason why (Steinway) Lyngdorf creates their subwoofers rather as ‘high bandwidth woofers’, so they can really cover the complete LFE frequency bandwidth range and even more then that. So they are always operating in their comfort zone. They don’t work almost good enough at 120Hz, but they fully cover the bass range. You can cross it at 100Hz or 200Hz, they’ll always play fine. This makes it easier to prevent a performance gap between the channels and the subwoofer and won’t make the subwoofer suffer from performance overload.
