Is an external 'why' needed? I don't think so personally.
Okay. Fair enough.
But I cannot get that question out of my mind so not everyone is inclined to worry about it as we all think differently. But I bet you some of your personal woes and depression you have is due to part of yourself asking this question. Only to end up being mutilated by your own convictions that no God exists. Now I am not saying that you "secretly" believe in a God, I am saying that you are secretly wondering why we are here and that is causing problems - an unidentifiable reason for some of the daily emotional pain most of us encounter. It's the infighting we have in our hearts when we disregard basic impulses due to belief sets.
Because let's face it. Atheism is also just a belief and it could also be wrong regarding everything. But the difference here is that I am not saying it is wrong.
Mutilated by my own convictions that no god exists? Good grief, I've never heard it put quite like that.

The majority of people in the world don't really think about this because they have an answer already, in the guise of one religion or the other.
I have no answer and I am perfectly fine with that, since I don't have reason to think that there is one. Aside, of course, from the obvious internal stuff like making the world a better place, trying to enjoy yourself, etc, etc.
You say that atheism is just a belief, well, that depends on how we might choose to define belief, certainly it is not a belief in the sense that Christianity is. To me, atheism is a simple statement about a reality for me that does not need any form of god involvement to make sense.
Secretly wondering about why we are here? The why is easy and not particularly bothersome, it's the
how that causes me sleepless nights.