There is no simple answer. Essentially, it is because there is no one willing and able to put out the fiendish amount of work needed to run one.
One of the reasons is that an 8th Association was not started after WW1. This means that when the troops returned after WW2 (and just wanted to get back to their former lives) there was no organization already set up for them to join. Other factors are the amount of fighting and casualties the 8th took in WW2, and possibly being a Regular Army unit had something to do with it.
Jump ahead to the 1980's, and a former artilleryman Jim Wooley. Jim took it upon himself to start and run the 8th Division Association. he slaved at it, and did a bang up job. Sadly, Jim became ill, and there really was no one to fill his shoes. Many elements of the 8th have their own, smaller regimental/battalion/company Association, so veterans are directed to get in touch with these groups instead of a large Divisional organization.
Looking at some of the larger divisional groups (1st Div, 29th Div, 82nd div) I find it a bit sad that the Pathfinders do not have their own Association. Maybe someday someone will have the time, resources, and energy to pull one together.
As I get permission from the various elements, I will post the contact names and address here. As for Historical questions on the Division, I've been handling some of the queries. Call me the honorary acting divisional historian, (unpaid).
The 8th did a small paperback book after WW2. It has been reprinted by the Battery Press. Contact me for more info. If the demand is there I'll have a small re-printing done for vets and their families. The various elements of the 8th had a series of large format blue hardcover histories printed in 1945. Known books are the 13th, 28th and 121st Regiments, and Division HQ and Special troops. Some of the Arty unit did their own histories- I am not positive which ones were actually printed. These are rare and hard to find. I am trying to find a 121st Regt book at a reasonable cost.
Write to me: Jonathan Gawne