...so what would be the reason for further litigation regarding the '336 patent?
Answer: To get money from it from those who refuse to pay voluntarily.
As to the U. S. legal system, each lawsuit stands on its own merit, which means that the rulings during each matter and the result of each, as with the HTC claims constructions and jury verdict, are not definitively binding on different defendants in different cases. It simply must be that way, because the converse is obviously unfair.
If you were the owner of a company that was alleged to be an infringer of the '336, would you want to be bound by what occurred in the HTC case even though you had no participation or voice in that outcome? And if we were to accept the resurrection of the Kessler doctrine, which would result in ITC rulings being fully and forever dispositive of the issues against even those who were not a part of those proceedings, PTSC would be forced to fold its tent and close its doors.
The idea of "one ruling for all, forever" certainly sounds wonderful, and it is --- as long as you're in the winner's position. And there are problems even with that, which I've addressed before, but further discussion of such would be beyond the scope of this post.
