Why do organisms have the urge to pass on their genes even if it is expensive for the individual?
I'm sure this question gets thrown around a lot here but none of the answers I've read so far have satisfied me. I understand animals reproduce because they have a primal instinct to make new generations, pass on their genes. But why? From an evolutionary perspective it's expensive to make children and provides absolutely no benefit to the individual
One argument I saw in a sub reddit was that animals that didn't have the instinct to reproduce don't exist today. Another dude said bigger numbers are beneficial, for instance a pack of 6 7 wolves as compared to just 2 3.
But even then it doesn't explain why animals that do it, do it. And as for the second argument I'd counter argue with the example of fishes that never care about their young once they lay eggs or the example of mayflies that die just 2 days into adulthood with their sole purpose of mating.
If we were talking about humans, at the very least we could say that certain people like kids and want to take on the responsibility to raise mini versions of themselves, but that ain't all true for other organisms.
So the question remains: Why do animals bother passing on their genes and establishing their presence in the world?
EDIT: Thanks a lot for your responses. I have a much clearer understanding now. People rightly pointed out that I mistakenly said it was expensive from an evolutionary perspective when in reality I was just thinking from the pov of an individual. But yea I think get it now