Why so obsessed with bass?

If set up right, a little bit of added bass will make the music more full and ambient. Try to add a sub at the center and closer to your listening position if possible.

I have heard that having a 2" thick piece of granite or bluestone cut to the size of your downward-firing subwoofer's footprint and then sitting the sub on top of it will improve bass, the idea being that there is more and denser mass to the stone than the wood floor underneath, with the added benefit that it will keep the entire house from becoming a transducer.

Does anybody have any thoughts about this? I am considering it.

Kitchen island good place for sub. 

Such a obsession to deal with bass issues.  Why is this?

The ability to control the extra low frequency is just plain fun for me.
  

On a sub if there is too much rumbling simply turn it down.

With proper room placement and modern multiple equalization parameters its possible to increase the extra low frequencies while controlling the subs unwanted nature.
 

As far as mains these probably are not much of an issue for most of us.

Probably not for many but being obsessed I enjoy that brief sense of conformation when I see a statement full range speaker being demonstrated with subwoofers.  

However for bookshelves speakers it makes sense they really aren’t well designed for lower range frequencies.

True, but with the right program material I've been startled by more affordable small two-way speakers than I can remember.
Watch out for that deep rabit hole. 

last time i checked bass and sub bass were part of the audible audio frequency range :) arent we obsessed with how everything sounds?

but seriously bass is the most difficult part of the frequency range to reproduce to an audiophile extent. it requires the biggest speaker drivers and enclosure volume, the most amplifier power and is most prone to room boundary and volume interactions, non linear reflections and frequency cancellations.
get it right and it is rewarding as heck.  
and you ask why the obsession?