Just like every other genre, VN can have elements of other genres mixed in.

I never saw the appeal of flying simulators, but yet they are here.

Edit. Or platformers. What is up with people playing those?

But flight simulators are actually games.

And they don't need japanimation nudity.

Presumably it is not the type of product that they wish to sell here if they're refusing them.

Yet they accepted Hatoful Boyfriend? The idea of dating birds made the genre closer to their standards?

With arguments like those, there is no hope to have a proper discussion with you about the matter.

Oh well, not like you could convince me they need to be here anyway.

They are probably afraid of ratings and the misconception that VN=dating sims. In the past most VN were adult oriented, but now that's not the case, granted there is a tons of bad VN out there, but there are quality products with complicated story, different endings, RPG elements, voiceovers and without adult content so GOG should begin selling those.

I believe that is unlikely, but for good reason IMHO. In order to specify an acceptance criteria they would have to codify one in writing and they may not actually have one in writing with a set of specific rules. Even if they do have a specific set of rules written down or not, they likely consider many different factors when deciding about a game, and such 'rules' will likely not be applied in a black or white manner but rather with discretion of one or more individuals based on numerous factors that can't be documented in a clear algorithmic manner.

To publish a clear unambiguous set of rules/criteria publicly would have every gamer who is in love with some game and wants to see it show up here angrily challenging why their favourite game fails some rule or another and pointing out that some other game that is here doesn't meet the same rule or whatnot. Also, they're free to change their criteria over time based on any reason they like, so any rules may vary over time and that may or may not be applied retroactively etc.

The worst thing they can do IMHO is publish a set of general rules/guidelines they use as it would just give angry people ammunition to throw rocks at them over some decision they make and "justify" why they refuse something. They're better off IMHO making decisions as they always have, and if the community shows enough interest in a particular title they sometimes change their mind too. If there's one thing I've learned as a software engineer over the years is that explaining the decision making process or a given decision to people even with the best of intentions often just gives them ammunition to argue with you and kick sand in your face if they angrily disagree with the decision. Sometimes explaining things is good, and other times it is something you wish you never did after the fact but can't retract.

While the point is valid that they have no reason not to refuse VNs, there also seems to be no reason to do so. I find it odd seeing as how there aren't so many companies willing to sell stuff on GOG so they probably should take what they can get, assuming naturally whatever it is isn't an unwholesome piece of crap of course. not to mention, I don't see why not as it diversifies the portfolio and I don't see too big a difference between a lot of adventure games and VNs.

But, I am curious what other games they should try to get beforehand. I know I'm holding out for Army Men and Vietcong.

Oh that makes me sad, I was hoping for more VNs here on GOG. :-(
Just yesterday I was asking myself whether I should be the current VN bundle on Groupees or wait for new VNs on GOG, well that question is answered now.

It's also possible that the few VN's they have here just didn't sell well and figure they just aren't something worth selling at this point.

I would like to see visual novels here. I never understood the rejection of sex in video games but the embrace of violence. And I'm guessing visual novel's reputation for involving sexual themes are the reason they are absent.

Just because a game deals with 18+ material doesn't mean it's a bad game either.

Hatoful Boyfriend - Around 120k steam players

Long Live the Queen - Around 213k steam players

Loren The Amazon Princess - Around 25k steam players

ToA: Seasons of the Wolf - Around 3k steam players

(Sorry to use your games jack_norton but it was the ones mentioned here by you)

I'm guessing it requires a certain level of sucess so that they accept the games here...