I mean... in print novels, Romance is by far the biggest genre. Print comics don't provide nearly enough Romance for how much market demand there is (largely due to misogyny and stuff...), so everyone who wanted to create and read it looked to the internet and here's what happened.
The reason Romance sneaks into other genres is actually pretty funny because it kind of originally emerged in modernist media as a "no homo" thing.
So in standard western 3 act structure storytelling, there is always a B-plot, where a character emotionally inspires and supports the main lead. Just around the start of act 3, when the protagonist has had some kind of big failure or defeat and is at their lowest, this character will turn up and there's a tender scene where they give the protagonist the emotional support that causes them to have the breakthrough they need to solve the problem in the finale.
Now, this B-plot character doesn't have to be the opposite sex to the hero, but because their interactions with the hero tend to be very emotionally nurturing and happen when the protagonist is in an emotionally vulnerable state and has to finally be honest about their feelings, it may come across...er...a bit romantic... regardless of what gender you make that B-plot character relative to the protagonist and often very unintentionally. So you get that whole thing in Lord of the Rings, where lots of people ship Sam and Frodo because Sam is Frodo's B-plot character and they're very vulnerable and emotionally intimate.
Because some people get uncomfortable with their protagonist being potentially being read as even a little bit gay, and because a lot of people want to have a cute girl or hot guy in the story for variety or eye-candy, and because a romantic partner being in danger can be a really easy way to motivate the protagonist and then getting love as a "reward" feels like a solid happy ending (like how Shakespearian comedies end with a wedding. In fact in Academia, ending with a wedding is considered a discinctive factor that defines a Shakespeate play as a comedy and is part of why Measure for Measure is considered a "problem play" that can't easily be classified- it ends with a proposal, not a wedding), people just generally started throwing a Romance subplot in there because it works. Which naturally made it a common story device or trope and then people started playing around with the genders because that's fun and allows people to do the trope in a way they can relate to or find appealing. Why not have the princess rescue the prince and fall in love? Why not have a princess rescue another princess and fall in love? etc.
Inevitably some people are going to shoehorn Romance into their work purely because they've seen it in other things, without really understanding the mechanics of how a good romance plotline works, how to make it actually add something to the story, or how to write compelling characters the audience would want to see together, but that's no different from people branding their protagonist a "villainess" without really using any aspect of it to enhance the plot (or even making her remotely villainous in some cases), or shoving a narration crawl about the ancient history of their setting into the opening of their story that just slows everything down and wasn't necessary. There are always bad writers throwing around tropes and devices they just don't really get or lack the skill to do well.
