If the Greek NT was filled with players from Niki Volos, OFI, Ergotelis, Kavala and the other clubs under financial stress then logically they may well not to be motivated to play for the national team as they aren't getting paid!
However this is NOT now not never been the case.
Did the Venezuela players fail to progress past the Quarters in the Copa America because their country is facing hyper inflation where a carton of eggs costs $200??? No!
The majority of the Greece team were not based in Greece. This is not a factor.
It's not even close to being plausible.