Sure, but cash is also an important privacy protection and if tax evasion is the cost then it's worth it. A society without cash is impossible to have true freedom of association.
Extremely high tax evasion (as in Greece around the financial crisis) can be absolutely debilitating for countries and their economies.
Privacy doesn’t mean much when you have 40% unemployment and people can’t get jobs to feed their families.
I also highly doubt it’s an easy hypothesis to test. It’s not like you can set up an experiment. Good luck linking correlation to causation given the highly unique conditions in every country.
For somebody who is not so familiar with Greek history: What are you referring to here? What was this scam you're speaking of?
This is a 100% for tax evasion reasons, and the "official" motivation is that "shop owned should not be forced to pay fees for card usage" - a very stupid reason, given that it is mandatory for the average person to receive his/her salary on a bank account. Most banks only allow you to withdraw cash for free on their ATMs, and extol a high fee otherwise (a fee that is several orders of magnitude higher than whatever a shopkeeper pays with SumUp or similar services).
The point is simple: employees either don't vote for the right or they do vote for the right due to rampant misinformation about social issues (immigration! Europe! LGBT!). The Italian right is basically a well run scam, they blatantly lie to the public in order to be voted in, then they inevitably do some nasty stuff to help those they owe favours to, before getting inevitably shredded the next election. In Italy if you are a political party you only get ~3y to do your stuff before being destroyed in the next election, so most people in politics are just in for the short term.