It's because the subwoofer is the domain of the enemy, home theater. Home theater represents everything that 2 channel does not. It's quantity over quality. 2 channel audio is all about quality over quantity. Home theater is for the ignorant masses that think big explosions are just so freakin cool they can hardly stand it. Because of the cromagnon target audience of home theater, subwoofers need not have any kind of fidelity. They just have to be loud and vibrate a lot. So, subwoofers got a reputation among audiophiles for being total garbage (and the vast majority are). Are there good ones, yes. Can they work in a 2 channel system, yes, but its not easy. Low bass is by far the hardest part of the frequency range to get right. That's why you see a lot of audiophile speakers don't even try to deal with sub 50 hz.
Why are subwoofers so polarizing?
I will admit I have never been a proponent of subwoofers in a 2 channel system. Maybe i've not heard the proper set up or the level of sub was not equal to the speaker. The last great application was over 20 years ago when I heard a Pro-Ac Tablette with a forgotten subwoofer. I'm sure in the last 20+ years the technology has improved but why are subs still mainly limited to home theater systems? As always I appreciate your time and thoughts.