I specifically said it wasn't wrong.
I don't know if I make a distinction between "stopping a player from doing something" and "thinking about the world and applying basic logic". I mean, I get that your goal is the latter, but the former is an outcome.
Two things on this.
First, this is your setting and you've designed it this way. Again, that's perfectly valid. But this is you deciding to place more importance on the idea that the giants of Jotunheim will never ever treat with humans or other mortal races. That they have a monolithic view of mortals and a unified response.
Second, you could decide that there is such a giant... perhaps an outcast of some sort, who will listen to the mortals. Perhaps he has an agenda of his own... he wants to reclaim his place in giant society... whatever. Here's a powerful group of mortals who may be able to help him do so.
You certainly don't have to do that, but you could. It's a choice not to. Neither choice is wrong, but they have implications about player agency. It's really that simple.
I mean, I've said repeatedly that anyone can play any way that they like, and there's nothing wrong with any of it.