q

If you don't care about VN genre clarification, skip down to the second-to-last quote. :)
tl;dr version, non-romance-route VNs aren't unusual, and as a rule turn out to be as reliable as VNs which have such elements.

Usually VN is about the romance

That's a genre thing, not a trait of VNs on the whole. Romance-based genres are not only the most popular and thus heavily released ones over in Japan, they've disproportionately been the ones exported out internationally. As an example of similar perspective, K-Dramas ([South] Korean Drama shows) are not only hugely popular within their own country, they also have massive international presence. And yet, South Korea is also known for its horror genre, which emphasizes character emotions over the gore-emphasis of western horror. Likewise, the country unsurprisingly isn't limited to just two genres of film-making.

VNs are the same way- relationship-based genres like Otomes, Dating Sims, and Eroges dominate, and are especially prevalent internationally- but they're still only just representative of their own genres, rather than the overall content style of the entire medium which they represent.
VNs are possessed of all the usual genres you'd expect from a medium- mystery, horror, action, comedy, sci-fi, adventure, tragedy, slice-of-life.. there's even Iyashikei, which is basically the Walking Sim genre of VNs (ie, take it slow, relax, and enjoy the scenery) though they tend to differ by having a reliably positive vibe. VNs may have a few genres and stylistic approaches which stand out in popularity, but as with most any film or book or gaming medium, they tend to be rather rich and vibrant in the overall breadth of genres they cover. While their genre emphasis may differ, they can be compared to anime (with which they often intertwine franchises), film, or more traditional novels in overall scope.

After all, VNs are just a way of displaying a story, rather than a strict guideline on what kind of story needs to be told. :)
[And, while far, far, far less developed a medium, the same theoretically holds true for Motion Comics, which stand as a western parallel to VNs- though by this point, the medium has mostly been used for straightforward comic adaptations. :X]

routes

Branching routes are similarly just a stylistic approach, rather than a universal inclusion of VNs. Linear VNs and Kinetic VNs are both also potential ways of presenting a story. For those that view VNs more as art-rich novels, over games, it's even a preferable approach to story-telling (especially as a single well-told story can often have far more impact than a story diluted with the mechanics typically involved within branching-path stories).

the writers will have to expand a lot of alternate or side stories for any branching plot choices since you know, the anime is linear.

From one of the curator reviews:

All together I thought PSYCHO-PASS: Mandatory Happiness was very good. Every choice you make changes the outcome in the end so be very careful with what choices you make.

Sounds like they've got you covered. :)

So far from the truth! Danganronpa 1 & 2, Steins;Gate and Nonary Games off top of my head are all stellar VN's which do not push any romance options on you.