Why do drugs again?

I'm not a felon but I've been around a lot as my mom was a lawyer. I also don't know how I got here but it seems like every other post is a question about when they are going to be drug tested or asking about of xyz will show up in a drug test. This is prompted by one of, in my opinion, worst offenders. The people who are ending parole and worried about a final drug test before doing drugs.

Like my man, I get addiction is a thing but you've already been sober throughout your whole parole. Why not just lead a sober life? I'm not saying weed is bad for you but your so separated from the life you had before becoming a felon? Why not love yourself, your body, and in turn your sobriety?

I just legitimately don't get it. Can someone help me understand?