I'm betting the reasons the Growler sales went poof is that they both want to ensure fleet commonality for operational and budgetary reasons and when the Super Hornet didn't win the competition a big incentive to buy the Growler went away. It would be a hard sell for Finland to buy a squadron-sized fleet of a completely different type than their main combat aircraft fleet, adding a good amount to their long-term operating costs.
Germany's decision had a significant political component but even then it makes sense to them for several reasons. They were considering Growlers in large part because they were looking at getting Super Hornets as well, and the big reason they were looking at SH's was they needed an American aircraft to maintain their nuke mission after their Tornados are retired and we are unlikely to certify the Eurofighter to do the mission. The big problem is the SH's aren't certified for the nuke mission and it would have taken time and (German) money to get that done while
F-35's are most of the way there, bought and paid for by us.
Given that very few air forces have tactical electronic attack aircraft, less than a literal handful, it shouldn't be a surprise that smaller air forces would chose not to buy them along with other enablers like tankers and AEW aircraft.