There is absolutely no logical reason why the two words should be used in a different way. I could say that "the same" implies the same sort or same thing, but there is no reason that is not true of "different". The final answer is that languages are not always logical. They have a life all their own. BTW, I strongly disagree with Eliot. Part of the trouble with learning any language is that you don't always even know which questions to ask. There is never any harm in asking and many questions (but not all) about language do have some logical answer

"The same" is specific. You're basically saying, "they are the same thing" or "they are the same as each other". The "what" is implied. Expand the phrase with different then you have "they are different thingS". You are being non-specific because... well, they are not the same. :)

Because we do. Why do you keep asking these kinds of questions? They don't really help you learn the language.

As a rule 'same' ,whether it is an adjective, adverb or pronoun ,it is always used after 'the' ,'this','that','these', 'those' etc.. However in informal English it could be left out" Let's meet tomorrow, same time." So it is a rule,that I don't know how to explain further,it might have to do with the syntax of the sentences.