Even ignoring the absolute absurdity of there being absolutely 100% no verbal exchanges in any way shape or form between any troll and any member of any race- do you think a sternly worded letter or statement is going to get determined invader to accept that they are forbidden from and not welcome on any particular piece of land?
The trolls respond with axes and fire and are met with pretty much near eradication so long as they continue sitting on a patch of land others want.
The Darkspear joined the Horde, who went on to conquer lands and wipe out peoples on Kalimdor and Eastern Kingdoms- and made to feel terrible about it. Although in order to do so, they had to give up a bunch of traditions and self determination.
The Zandalari actually seem to have accepted Vulpera and Tortollans living on their island, although they do so “by the grace” of the Zandalari. The Zandalari have, however, made it clear that they will not tolerate any infringement on their sovereignty by the Horde. Talanji doesn’t hang out in Orgrimmar like other leaders. Their forces even seem to operate independently of the Horde’s forces, rather than as a part of it.
And no, it’s not just the Alliance either. It’s just mostly them when it comes to trolls because all the troll tribes exist in what’s now the Eastern Kingdoms, which is where the Human, Dwarven, and Elven cultures flourished. But as mentioned before, Thrall was all too eager to throw them under the bus, and Horde forces also join in when it comes to driving trolls out of Arathi. Blood Elves and Qul’thas became part of the Horde, and they still fight with the Amani over the territory they took centuries earlier.
There’s also Stranglethorn Vale, where Horde, Alliance, the Steamwheedle Cartel, Venture Company, and Pirates have moved in to settle/exploit the region for its resources, defile ruins, and slaughter the local troll tribes whenever they get in their way.
Zul’aman has been covered.
It’s not that various troll tribes don’t have anything to gain by allying with outsiders or inviting them to settle amongst them. But in instances when they clearly don’t want to, it’s not unreasonable that they’d want that to be respected on some level and aren’t monsters for it. They certainly aren’t deserving of being slaughtered and pushed off their land and treated like nuisances.
But the game rarely ever frames it as such.
The Horde does some introspection. There, trolls are more likely to show up as something more than monsters and loot pinatas and the game kind of sometimes explore the consequences of this. Being a troll and fighting other troll tribes over territory and troll matters also has a different context compared to being a troll and fighting night elves or humans over territory.