The bottom line is that there is no specific reason to design a center channel speaker that can go below 80 Hz.
To understand why you need to understand the whole logic behind bass management and small speakers in the first place.
Our ears are very effective at localizing frequencies above 100 Hz or so (we can hear where they're coming from).
Therefore, at higher frequencies, where each speaker is located, and things like toe-in, are very important.
For this reason, at frequencies above 100 Hz or so, we need to be able to position each speaker "where it belongs".
At frequencies below 100 Hz or so the exact opposite is true.
In general we cannot localize those frequencies well at all.
And, in addition to that, frequencies below that tend to be strongly affected by room modes and room location.
And, in addition to that, if you have multiple speakers making those low frequencies, they are very likely to interact with each other as well as the room.
(And, in many cases, the ideal locations for speakers producing frequencies below 100 Hz are quite different than the ideal locations for other speakers.)
Therefore the logic is that by separating the frequencies...
- you get to put the speakers reproducing the higher frequencies where they need to be so the sound they produce "comes from the right place"
- you get to put the subs, making the lower frequencies, WHEREVER THEY HAPPEN TO SOUND GOOD IN YOUR ROOM AND WITH EACH OTHER
If you have large front speakers you have already complicated this situation... (because they are each now a source of low frequencies)
The reason this is a problem is that, in order for them to sound good, you MUST put those front speakers in certain locations.
They must be located where the mid and high frequencies balance well and seem to be coming from the proper directions.
HOWEVER it may turn out that this location is NOT good for their bass response...
And it may cause them to interact in a bad way... with the room, or with each other, or with your subwoofer or subwoofers...
However, because many people use those front speakers as full range speakers for playing music...
This is quite often considered to be a reasonable compromise...
But, for most people, it is NOT considered to be a worthwhile compromise for their center speaker...
Most of the useful contribution from a center speaker is for things like dialog...
And, for that, the mid and upper frequencies are the most important...
And most people prefer a center speaker that is at least of limited size...
And, if your center speaker were to be full range, it would essentially be "yet another subwoofer that may interact badly with the room or all your other subs"...
(Yet, at the same time, since it must be placed where it belongs, you cannot adjust its location to optimize its bass response.)
Taken together these facts all lead to the conclusion that a "small" center speaker is more useful and more practical.
And you gain very little by designing or using a center speaker will full bass response.
And, for that reason, almost all center speakers are designed to be run as "small speakers"...
Note:
There is also a valid argument that "if you have the room, and the budget, it's best if all of your speakers are the same".
However, unless you have the space and the budget for all large speakers, that argument rarely wins.
And it really still doesn't justify a large center speaker that is still different in design from the other speakers.
(And you really can't just "lay a big tower on its side..." because that results in an asymmetrical left/right dispersion pattern... which is bad for a center.)
Did they make the speakers?
But they are the experts on HT and most HT enthusiasts seem to agree.