Difficult to implement properly. You can set code to say "ball touches hand = foul", but that's not the full rules of the game. On YouTube, watch a Mark Goldbridge penalty compilation (on Fifa) and see how many given for handball looks dodgy
If they could do it 20 years ago why not now ? We now have better technology and i see no reason why not implement it. It wouldnt be perfect or maybe just a gimmick but id be nice to have "new" feature. Even in real life a handball foul is never 100% correct.
Honestly, they just lazy.