Yea the most time consuming part is the art. The game has a different paths and choices that he has to take in consideration when writing the story but it still doesn't justify the wait time between updates. The real reason for the delays is that he spends most of his time playing video games and arguing with people on twitter.
I think redners define amount of content these game can produce in time.
That I thought only limitation
Writing itself isnt rocket science.
First chapters intoduce girls, than start slow harem building by making MC spent time with each girl one on one, and slowly preparing them for idea of potential harem.
Than when each girl virginity taken, than well time to start doing FFM, split girls on pairs and make them pork MC in pairs.
Than when that done reveal them it actual harem all alon, by time they all broken and hooked on MC so much they just accept.
Than somehow create ending to legalize harem: MC marry one of girl, while other conqubines, or he bought huge House where he live with those girls, or went to Island where polygamy allowed.
Or something like that
Than amount of solo dates with each girls before FFM happen, demand on how much renders can be produced.
Making these dates very easy from writing style: each girl could have her own type of date depend on personaluty and allow slowly build some relashionship with MC.
So well that it.)
Ading branching stories arent that hard since MC was gona go on these dates with each girl anyway. So just block other dates and harem route for girls who arent in harem. Make them good friends, and maybe even hint they still hook on MC even if he reject them. Than add some unique ending for solo route, and that it.
As for sex scene get yourself horny, drink some cofee and start write them. If girl is hot any sex scene would be like. Can add some extra kinks for guys with fetishes, and that it done.
Like I said it could have been done in few weeks. But render it all, hours and hours especially with animations that where true chalenge is.