Why so obsessed with bass?

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?

I hav eno booming bass, but do have a matching dedicated amp and preamp.  Recently, I had to listen to just my mains to reorient myself to just how much bass I need.  The system does allow me to make old LP's sound much better, especially when I bypass the sub crossover to add harmonics to horribly mixed albums..

I caught one 9 1/2 lbs two weeks ago . 

Bass frequencies are essential . Even if you think there is no need of it as in listening to a female soprano. Speakers that play above around 60 Hz sound clear , clean , pristine.   When the speaker can  plays lower frequencies transparency and detail very often suffer. Reason being lower frequencies require care in speaker position.  Sometimes the speaker does not couple with room boundaries, or the room acoustics are unsuitable. Hence a limited low end extension speaker will sound better.  Takes time and patience to get the room acoustics treated and speakers optimally positioned .  When done right the sound just clicks in and all is good.  The same applies to subwoofer.  It is important to choose a full range speaker or stand mounts with subwoofer to match room size.  Then to get an amplifier to synergise with speakers. Too often we buy speakers without considering the room .