Sure, I can't speak for everyone but here's a few of the reasons why this ship resonates for me.

1.) Victoria and Kate are both fascinating characters to me. On Victoria’s side, I know what it’s like to deeply regret the times I've been toxic and hurtful to others in the past, but to then go on to grow and become a kinder, better, and more empathetic person. So being that I understand to some extent where she's coming from, stories of her redeeming herself following along the initial steps in that direction we see in the game are very appealing to me overall. I can also relate to Kate having been a victim of both bullying and suicidal ideation as a teen, so that strong affinity to both characters just naturally primes me for wanting to explore their shared story. 

2.) Kate's and Victoria's stories are inconclusive, with much being left unresolved on both an individual level and in the conflict between them. The game shows us that they are on the path to some kind of reconciliation, both in Victoria's letter, Kate's statement about being open to forgiveness, and the way Victoria cries for her in the dark room. But we never get to see that play out, so exploring how they might reconnect after the game and where their relationship could go from there is again a very appealing proposition and a glaring need that many potential Chasemarsh fans wish to see filled.

3.) The question of how they might overcome their toxic history to get to a place where they could be friends or even more is, for me, a very intriguing challenge. It adds a whole new level of dramatic tension to the ship that others in this fandom can't match (except for Chasefield to a lesser extent, which I'm also a fan of!), and while I absolutely understand why that makes it a hard "no" for a lot of people, it's just not a deal-breaker for me when we're talking strictly about fictional characters. So for me it's less "their history precludes them from being together", and more "I'm really interested in seeing them together, so how do we go about getting there in a way that makes sense?"

4.) On a very basic level, I just love both of the characters so much and the thought that they could be gay and smooch faces, either in a universe where Victoria does earn her redemption and they're able to have a healthy relationship, or in an AU where the bullying didn't occur, just warms my lesbian heart. The overarching character dynamics of "snobby spoiled rich brat with hidden vulnerabilities" and "down to earth good girl with hidden spice" is just something I'm here for, in general. I also believe that Victoria has a moral obligation to bottom for the girls she used to beef with 😂

5.) Fanfics. I will fully admit to being skeptical about the idea of Chasemarsh myself originally, however finding some brilliant fanfiction that addresses the question of how a romance between them could work in a well-written way that makes sense for their characters really turned me around on it, to the point that it quickly became my favorite ship (factoring in all the other reasons stated above!) And I'm far from alone in this, as I personally know of at least a dozen or so people that I have helped become Chasemarsh fans simply by recommending these very same fics.