Because antidepressants do not cause you to be happy. If you take an antidepressant and someone passes away you will still be sad, if someone yells at you your feeling will still be hurt and you may cry. So that is not how to find happiness.

I think of antidepressants this way. In your brain there is one side making chemical and one side catching that chemical. There is either not enough being made or not enough making it to the goal. So think of it in terms of basketball. If you need 100 baskets to be made every hour in order to "feel" happy and only 40 are made then you are not reaching happy. Some hours your brain makes 80 baskets other hours it makes 20. It is just never enough. Antidepressants make the basketballs stronger and makes them have more power, it makes the hoop bigger and gives you 50 extra balls to boot. So now it is more likely that they will make it to the basket and with 150 balls there is a greater chance of making that quota of 100 per hour.

In technical terms not enough neutrons are being made and fired and received every hour and it takes that for us to have the ability to be happy, but it will not MAKE you happy, that still comes from with in. But with out those neutrons there is just no way to even begin to allow your body and mind to even attempt to create that happiness.

I have depression by the way and take antidepressants. Sometimes I need to up the dosage with the assistance of my doctor. I have to find the right balance for me. Sometimes what works for a few months no longer works and you need more. Sometimes the antidepressant you are given is not the right one. (it doesn't make the basket bigger so it can receive more or it makes the balls stronger but not strong enough)

I hope this illustration helps you or someone understand how that works a little better. I have to take things out of the scientific context sometimes and make it something I can envision in order to understand it.