They don’t actually, not like us. I can’t go half a mile in any direction of my house without running into at least one American flag (which is awesome!). Most car dealerships and shopping centers fly them as do other business. And sometimes you’ll just walk down a street lined with them. However if you go to any European country you’ll typically only see them on the official flag poll the city put up. Merkel even famously removed a German flag from a photo shoot because it was not political to be proud of the flag.

My belief as to why this is is that other countries have no real reason to be proud of their country. Their flag’s image doesn’t evoke feelings of freedom like our does. And of course a constant complaint of theirs is that we fly our flag too much, but that’s just jealousy that we have something to fly for.