If memory serves, in X2 he did the scar thing for each of his sins.
It was a very, overly religious thing, which fit that version of the character.
My hope, and I believe many other's, was that this younger version of Kurt, in this new timeline, wouldn't be the overly religious version of the character, you know, the type that would scar his body to represent his sins.
For me, it's difficult to see Kurt as both someone who would be willing to scar himself for his sins and be the fun-loving version that many of us love. And it's really tough to do both. You can't be the overly religious version from X2 AND be fun-loving and swashbuckling.
And to change the motivation behind the scars representing his sins to being, maybe, something he thinks looks cool, would be beyond stupid. It would be akin to Singer and Kinberg just ignoring prior, movie canon, but I have a feeling those two don't really give a hoot about maintaining an appropriate timeline (for example, how can Warren be in this 1983 movie as a teenager, when he should be a newborn?????).
They really should have just left the stupid scars out this time...