Why 'wish you the same'? It sounds so drab, dull and unemotional. Why can't the person addressed to respond with a return 'Happy Dassera/Diwali/New Year/whatever'?
Sometimes fads like these catch on and it actually becomes fashionable to do such stupid things. When the person has wished us let's say with a 'Happy Dassera', we can easily say, 'Happy Dassera to you too!'. Now, what's wrong with that? Sounds so much better than a 'Wish you the same'. Or even worse, a 'Same to you' which throws out even the 'wish' part of it!
A greeting is a nice way of wishing someone. Add a smile and you have contributed to building a lifelong bond with the person. It should be genuine, heartfelt, warm. And 'Wish you the same' kills all that.
It is used to avoid being repetitive, did I hear you say? Rubbish! When someone says 'Hi', do we respond with a 'Wish you the same'? No. We return the 'Hi'. Then why not respond with a greeting when someone greets us?
And yes, Happy Dassera to you! (Don't you dare say you-know-what!)