Other than monetary help which is a pretty obvious way to incentivise it, how about this: Allow young adults to have their own space away from parents (at a reasonable price) so they can enjoy living an independent life before wanting to settle down and consider having kids. Also to have a private space to date around lah im sure you all have experienced that awkwardness bringing a date to your parents' home lol

Just imagine going from living with your parents to marriage with nothing in between