Shouting in Japanese at restaurants

What is the reason that waiters and waitresses greet customers by shouting in Japanese at Japanese restaurants in Taipei? This phenomenon transcends food types, whether it's fondue or rice and dish. Taipei has the most diverse restaurants with cuisines from all over the world. But do you hear people shouting in Portuguese at a Brazilian barbeque, in Italian at an Italian pasta shop, in Cantonese at a dim sum restaurant, in English at McDonalds' or T.G.I.Fridays? For whatever reason, this is an unsymmetry.