Ok first of all I think that ppl who dont believe in an afterlife dont have motivation for life but keep on living because there instincts are to do so. Its a sort of bio-mechanical natural response of such, they are also taught to by parents and such. Thats why ppl who are suicidal have broken what they are naturally trained to do, which is to survive.
Secondly an afterlife to atheists isn't nescerally heaven/hell. It could be any form of consciousness which may not be in a heaven or hell form, these sorts of thoughts are what can cause phobias aka therapingdragon.
Thirdly I do believe in an afterlife of heaven and hell. I believe that the motivation towards life is that I need to get as many of my freinds and family and enemies and strangers and anyone I can, to go to heaven and not hell through Jesus Christ, not just being good or bad. That is my answer for the question of the meaning of life.
To answer the question directly, people who dont believe in afterlife live for worldly temporary motivations (money, power, fame). These aren't nescerally bad things but dont go with you when you die.
Other motivations can be family and relationships these motivations aren't bad motivations but aren't permanent enough to base your life upon. People die, relationships break ppl get divorced. As soon as that happens your motivation for life may dry up and then what you kill yourself?
I recommend a permanent motivation which cant be found without a belief in an afterlife which unfortunately is not part of the question.
I hope this helps A2, good luck with your essay.
In the future I'm defiantly going to ask you guys for essay advice on my next essay when school starts
