Originally posted by Jitatha:

I recall devs saying they would not be putting a ladder in for various reasons, cant remember why though or where.

I fear this is as close to an answer as the OP is likely to get, at this date, from Iron Gate Studio.

Having given its reasons for not having vertical ladders once, Iron Gate Studio has moved on. One could search Discord discussions, social media discussions, and the development blog on Steam if one cannot understand why vertical ladders are not in the game.

Of course, one would actually have to make an effort to do so.