I can't answer why are we alive, but I can tell you why we chose to continue. Because like some cliche quotes would say, "Life is a journey" or "Today is a gift, that's why it's called present" even if those quotes are overused, it doesn't mean that it is not true. Remember when you were a kid, trying to learn a new skill(riding a bike/swimming/speaking a new language), it at first but because you are living and life goes on, you finally overcome the hardness and gain the skill. And you would look back at how helpless you were before. When you go to school, even if you don't like it there and can't catch up with the subjects, remember the times when a weird guy did something silly in class and everyone laughed, remember the times when you would imagine a shooter entering and how you would save the whole class. Sure at first those memories are just new experiences but after a while, you can look back at the good times and know that life is worth living.

Basically what I'm trying to say is, there are bad times, there are experiences that you hated at first,there are boring moments, but in the end the good memories and the bad experiences that turns out to be good memories would be the reason why people continue to be alive. Like another overused quote said "Appreciate the little things"