Marriage has taken place only when there is the union of body, mind and soul which can happen without any separate marriage function having been arranged which is called Gandharva Vivaham. Marriage functions these days are for legalising the marriage and for the knowledge of others failing which there will be tendencies for polygamy becoming popular.
Regarding Karma, one has to do it whether he likes it or not. We are living in Karmakanda and that is why we cannot sit idle for more than a few moments. Yes the lazy ones do attribute it to Astrology to safeguard oneself in front of others.