I think they can be sinful simply because of the passions they tend to arouse. I used to get so angry when I was younger that I'd take God's name in vain. That's never good.
Yes, I agree that playing video games certainly
can be an occasion of sin for that reason. Similarly, alcohol arouses passions in people with certain temperaments, and when consumed in excess. Likewise, physical sports can certainly arouse passions in players and spectators, not infrequently leading to physical violence. I think we've all seen evidence of that.
But just as neither alcohol nor sports are
intrinsically sinful, neither is a simple game played by manipulation of electronic sprites on a screen. All of these things should be enjoyed in moderation - with especial moderation imposed by parents on children - and should be avoided entirely by those whose temperaments incline them to overindulgence or easy overexcitement of the passions.