This is not entirely correct. On one hand, these organisations represent a great many of the potential claimants -- I don't know about Bavaria, but in Austria, majority f members support the leaders in such positions. On the other hand, a significant part of material claims would have been collectively, communally (or state) owned property. *Lunatic*, n. One whose delusions are out of fashion.
They support that position but just because someone believes that there should be a settlement awarding only symbolic compensation doesn't mean they won't take more if it is suddenly available. The organizations have no authority to renounce that right on behalf of their members (let alone the majority of expellees and their descendants who are not members). Nobody does. People can oppose a policy as harmful to the general good yet still act on behalf of their own individual good if that policy is enacted.
On the other hand, a significant part of material claims would have been collectively, communally (or state) owned property.
Both Czechoslovakia and Nazi Germany were based on private property, there was more than enough to bankrupt any state that is suddenly made liable for compensating the expellees in full for their losses. Not that I can figure out how you'd calculate those losses - at 1944 price levels, adjusted for inflation or not, with interest, at current value of the property ...?