The watchtower , by their own admission was built on unsound foundations. This has been attested to by their rejection of ' the old teachings ' to which they no longer hold. Any structure built on shaky / inappropriate foundations will eventually to avoid collapse,have to be 'propped up ' therein lies the rub, there will always be those who will prop up or accept the reasons for such to maintain the survival of the original. Their investment ( for whatever reason ) is deemed too important to contemplate demolition.
Propping up = NEW LIGHT.