Cheap credit was certainly a factor but I don't think you can ignore the effect of the Plaza Accords, the forced appreciation of the Yen, and the forced transfer of semi-conductor technology from Toshiba to Intel and other US compamies.
Japan is not a fully independent state and was/is under effective US military occupation. That's why they had to knuckle under and give the Americans what they wanted but when America tried the same against China, China told them to go eat shit.
Fun side story: at the height of the bubble, one property valuer estimated the land that the Imperial Palace in Tokyo sat on was worth more than all the real estate in California.