Human nature is you want what you cant have.
why do we love people who don't love us back?
Hope.
That does not mean you should waste a lifetime waiting on someone. Part of loving someone is accepting them for who they are.
Love is an act that we perform. It does not require reciprocation.
Romantic love is a unique type of love, with its own set of requirements for such an act of loving to be rewarding.
One of those requirements is usually reciprocation---and we hope for reciprocation much longer than is probably reasonable.
In short
We're idiots!
I'm there .
Humans always want what they cannot
have.