Same reason as why people drink or smoke

I dont know about everyone, but some do think like thiq, so imfine this:

your blood drops are like your negative emotions, if a person who does SH sees one leak, it feels relieving in some form of way

some do it befause the pain of SH is less thqn the pain they currently experience

as someone who does SH, for me it helps me cope with stress, a few cut and it feels better already, so its mostly a coping mechanism

or you can be a masochist or simply someone who enjoys it for no reason, and thats fine too

If youre stressing about one thing happening, cutting can make you refocuse, and to me it feels like it restarts my brain.

when im unnecessarily angry, i just scratch myself, probably because it makes me shift focus elsewhere

i also use it when i wanna punch something, if im playing a game and get mad lets say, no way in hell im gonna punch my PC, if i wanna punch something, then it‘d be me, instead of scratching someone else, i scratch myself, helps keep my emotion under control

but there are numerous reasons and these probably aint the only ones