Any restaurant (esp. that serves alcohol) have their peak revenue days on Saturday and Friday while Monday is the slowest day. If the Nepali party organizers were to book such restaurants for Friday or Saturday, they will have to pay premium rental charge and the converse is also true. Assuming the intended cover charge is constant, the organizers try to maximize profit ( = revenue - organizing cost) by conducting the parties on Monday.

Parties are about having fun and not about saving money. I think the organizers need to muster some courage and pay premium rental charge for Saturday and make the attending patrons pay premium cover-charge in turn. Trust me, conducting weekend parties will get a revenue boost because of more number of able attendees from various backgrounds.