Why are most people attracted to the opposite sex?

Biological imperative for the continuation of the species.

That's all we get to choose from. We can't mate with animals so you might as well enjoy it!

Its called reproduction, Its how species keep from going extinct.

biology

Because opposites attract.

We'd all be extinct
if more people were homo
birthrate in decline

It's because the only way you can reproduce is by mating with the opposite sex, so nature gave you hormones that made most people like the opposite sex to encourage reproduction and keep the species alive. That's pretty much the purpose of life for most organisms, keep the species going. Humans don't really need to as much anymore. Not all humans need to reproduce to keep us going.

Our bodies and minds are designed to react with each others in certain ways - like two pieces of a puzzle (in many ways).

because you wouldn't be here to ask such a question

Women are beautiful. Duh.