Jai: Why does Manusmriti mention only 3 vedas?
Swami Ram Swarup: Atharvaved, Rigved, Yajurved and Samved i.e., all four Vedas, state that in the beginning of every creation, Almighty God originates knowledge of said four Vedas in the heart of four Rishis. So, it is eternal and unchangeable fact that there are only four Vedas. So, Rishi Manu or any other Rishi-Muni and learned person cannot state that there are three or five Vedas etc. When there is any mention about three Vedas then fourth Ved i.e., Atharvaved is automatically considered. You can quote the shloka of Manusmriti for clarification, from here, please.

Ramakanth: Namaste Guruji, IS THERE ANY SLOKA in vedas that parents especially father should not take money from there daughters after marriage>
Swami Ram Swarup: Namasteji. Atharvaveda, mantra kehta hai ki jab kanyadaan kar dee to us se koi dhan aadi nahin liya jaa sakta.

Jai: You say Krishna had 2 wives is this correct?
Swami Ram Swarup: Yes, Sri Krishna was a great Yogi and Brahamchari. He had two wives – Rukmanni and Satyabhama. Only Puranns like Bhagwat Puranna has told about several wives of Sri Krishna which is not mentioned in Mahabharat etc.