I’ve seen some Steve and Kayla fans say that they wish Kayla had gotten together with Marcus instead of Shane. Personally, I think the main appeal of this pairing would be the couple name: Karcus!
It’s no surprise that Marcus falls in love with Kayla. We saw how much he idealized the love that Steve and Kayla shared, how he always compared his own relationships to theirs and found them lacking. It was easy to see how he could go from “I want what Steve had with Kayla,” to “I want Kayla.”
We also saw that, after Steve’s death, Kayla depended on Marcus, leaned on him, needed him — more so than Shane. As he fell for her, she seemed to deliberately close her eyes to his feelings. I think she needed him so much she didn’t want to face how he felt, because that would mean she would have to pull back. (Shane called her on this several times.)
Later, as she began to fall for Shane, she seemed to regret that she didn’t fall for Marcus instead. This scene is actually a little bit later in our timeline, but it’s the scene where Mary Beth plays that note of regret most strongly:
She is obviously thinking that here is this great guy, so considerate and such a good friend; why didn’t I fall in love with him?
As to why the show didn’t pair them together, I think that there wasn’t enough drama there. Yes, it would be an interracial relationship, but I don’t think that would be enough. They were already very close, too close for there to be a journey to come together.
I also think it would have been too much about Steve, too much Marcus taking Steve’s place. Kayla later has a very interesting conversation with Shane (which I will do a post on later), where she says she didn’t think she could ever be with anyone because she will always love Steve — that it wouldn’t be fair to that person, to make them second best. One of the things Marcus always said was how much he wanted a Great Love. Kayla knows she could never give him that.