As far as the Muslims are concerned
If someones does you a favour and then you thank them, this is good manners, right? What about God who provides everything for you.
There are many reasons for praising God, I'll give you some God provides food, housing, health, security, water and many things you don't know. Especially living in the west, were most of us live like kings.
If you praise God it gives the soul piece of mind and light.