The teams don't see any revenue from the gambling money. The government does from legal betting companies. Lot of sports gambling in Greece is via online betting and a lot of it on illegal sites, which don't offer any tax revenue.
I agree that more money intro the league is good, but there are only 5 or 6 healthy clubs that can survive using the revenue from TV, tickets, etc. Under the current system people that put teams into debt and in some cases declared bankruptcies only to come back and created more debt. Instead of the owners being put behind bars and the teams dropped into amateur divisions they get rewarded with a TV contract using tax money that should be put into better use. As long as the owners see that the government will always be there to bail them out in the end, there is no reason for them to clean up their act.