It's deceptively easy to for a potentially erroneous impression of any culture from a surface analysis.
That equally applies to any culture – many countries’ populations think all Americans are right-wing gun carriers with nice teeth and a love of invading foreign countries. Or the British, with their miserable weather, rigid social class system, terrible food and drunken hooligans. And the Italians, with their greasy lothario men, and their big-bottomed women who shout a lot.
But impressions are just that – they reveal nothing of the reality of the way people live, or indeed their happiness and security in living a lifestyle that is familiar and safe for them.
So I wouldn’t worry too much about Muslims not having fun, or more accurately not appearing to have fun – they simply live in a different way to us.