It's not that easy
If the person behind the DoS attack actually knows what they're doing, it's much more than "oh let's just put your IP in this program I downloaded and run it on my home computer"
There's multiple types of DoS attacks, most use spoofed sender addresses, some are hard to distinguish from legitimate connections
And in the case of a DDoS attack, you often have a botnet (multiple computers infected with malware) and the bot master says "ok guys go attack this guy for me" and if you trace that IP back all you find is someone who's only guilty of not knowing how to secure their computer