The brain is a problem solving machine. In the absence of "real" problems it has a tendency to create some to have something to do.

Another factor is that in our ancient past social isolation meant certain death. So new societal rules stress us almost as much as a looming predator because if we don't follow them properly we could/ would be ostracised.

We also spend much less time in groups which gives us a negative impression of our social security which causes intense stress as above.

As an ex weed smoker of 20 plus years I assure you we're better off without it. I was also on anti depressants for around 5 years and I'm so much better now without either of those crutches. I view them as pain killers when your leg is broken, they help the symptoms but they don't do anything to cure the ailment. Only effort and a genuine desire to change bad habits helps in my experience.