Because they are purposefully highlighting it.
Yes, one single trailer out of who knows how many. Oh, the horror.
Mario could be gay and it wouldn't change anything or mean anything.
It actually would, because Peach clearly has the hots for Mario, and Mario seems reciprocal to them.
Yet people want more gay characters in the games for reasons, because a character's sexually makes them more relatable somehow. Which is fine, so give players the choice to make the character gay or not.
Except that's not how things actually work.
If you have a game like Mass Effect or Dragon Age, sure. Follow your heart to your own heart's content. But it's iffy if you're saying that games making the character hetrosexual is fine, whereas homosexual should entirely be in the purview of player choice. What's wrong with a creator simply saying "the character's gay?" Again, in Naughty Dog, no-one flipped out over CrashxTawna, or JakxKiera, or NathanxElena, but suddenly people flip out over Ellie. You only need one guess as to why, and that says more about the people flipping out than Naughty Dog.
If you are going to make a character gay, then write it into the story in order for it to matter. Like I said originally, Dina getting kidnapped could yield her as the "princess" that Ellie has to save and it'd be cool.
OR, you could write your story where your character is gay, and have that be part of their character, but not the definition of it.
I seriously don't get why your view is that any gay character in a game (and maybe other media) has to be defined by their sexuality.
Also, as an aside, "save the princess" is an old trope, and I'm not making the argument that it's "sexist" or "problematic," I'm arguing that it's tired. Again, using another Naughty Dog IP, Crash saves Tawna in the first game, but Coco came afterwards, and is much higher regarded, by virtue of being an actual character. It's part of why Mario games don't appeal to me on any level of story (oh no, Peach has been kidnapped again because she refuses to invest in castle security), while Sonic, for instance, actually transformed Amy from a damsel in distress to a character that...well, that depends on which Amy you're talking about, but at least a better one whose original purpose was to turn up, be kidnapped, and be rescued.