Personally i think every month can be too often for a small group or solo dev, they don't have time to put out meaningful updates in that timeframe if they are part-timers like a lot of first time devs, too much pressure and they burn out before they finish.
A lot of the devs who put out real quality, Philly, Motzkeys ect. will go for a more substantial update once per quarter or w/e, i'd sooner wait three months for a few hours of decent gameplay than a month for half an hour with two or three scenes in. Also there is pacing to consider, a dev who's updates are little and often will be forced to drip feed sex content whereas a dev who goes for bigger chunk, while still expected to give us the goods each update, can vary the pace a little better and make the sex content fit the narrative better IMO.
All that said in favour of larger and less frequent updates there are cases, especially with sandboxes, where small frequent updates can work well, look at Faerin and Baal(superpowered), small regular updates work well for them, so perhaps it's more to do with the type of game, i really do think that VN's benefit from larger updates rather than small and regular though.