I forget where I saw it, but someone from Allen & Heath gave an explanation.
Please correct me if I’m wrong on anything here, I’m going completely off memory from reading a post somewhere online a while back.
With that said, it was something along these lines:
The reason the SQ series sounds the way they do is the way the audio path was designed in it’s software. And because a great deal of attention was put into that, it isn’t as easy as people think to just toss a LPF in the chain without disrupting everything else going on. They do in fact plan on adding it, but it will take some time to properly implement.