I don't think it's that people don't understand what love is. I think that people often believe that the only kind of (platonic) love that exists is the kind they've been taught about. It's not a matter of personal intelligence. It's just that many of us have been conditioned to try to love our enemies, families and neighbors. The point I think Osho's trying to make is that the act of trying in itself destroys the possibility of true sincerity, and thus it can never be authentic love.