Because KSR/Obviousness is not a sure thing.. IMO the patents are very, very strong.. but I sure don't know for sure how KSR/O would playout thru litigation and neither do the Js nor TPL.  Given the more liberal definition the Supreme Court has recently thrust upon this issue.. this defense does have some teeth.. more than it did even 1 yr ago. 

Because KSR/O is not a sure win defense,  the Js still risk being found guilty, 'losing face' & treble damages via willfull infringement..  that's a big risk.. to the possible tune of $300-500mil ea, maybe more.. 

So.. they know they infringe.  TPL knows KSR/O is out there.. neither wants to risk a definitive lose... so, IMO, some where in the middle they will meet

jmo.. regards