Most major nations in the interwar times were democracies. They had a very hard time maintaining or even financing their armies as they historically were (except for Japan). That's why there is a limitation. Else someone will stockpile tac-bombers as belgium during the interwar era and then steamroll-bomb their 20-division army through germany in 1940. Feel free to deactivate those events by deleting them from the event files, though.