It was just a mistake it seems, but the density of forgotten beasts & megabeast attacks in mountain ranges are pretty high as it is, which makes some dwarf civilizations prone to losing the mountainhome & subsequent other market fortresses early on or going extinct & refugee particularly.
Dark Fortresses are also underground by site-type, but can't be targeted by forgotten beasts due to it being explicitly exposed to somewhere else down the winding paths. Its how they collect trolls natively with [USE_EVIL_CREATURES].
Q - What kind of conditions need to be met before companies* manage to shake hands with dwarves and set up a building belonging to another race in the middle of a market town?
Q - Do organisations present in other civilisations go any further towards the modularity of cities pre-site rewrite development goals? Much in the mind that a long time ago you released development pictures of how villages are formed out of preset pieces but arranged appropriate to population sprawl with space for fields etc. Now we have more structures like these warehouses placing themselves between everything.
*(to keep the answer simple rather than addressing other 'organisations')
I mention this because dwarves and humans tend to be pretty friendly anyway, building roads between one another and regularly taking in adventurer traffic compared to elves who are warlike over cultural dogma and aggrieve other civilisations against them for repulsive habits. There would be circumstances where through player interaction the company's trade would break down if the player took action though right?
The only other example where this happens I can think of is when enemy civilisations decide to build fortifications over a site, like goblin trenches (which don't really do anything to boost positional advantage last time i noticed) usually as a occupier, rather than a voluntary action with overlapping stakes & shares in a city.