I work as a mechanic for a living. That may have something to do with it. Stress with issues with life outside of work is probably another. I work 8 days on and 6 days off. I have 2 V8s to put together, but have no desire to mess with it. Those 6 days I do as little as possible and just chuck it in the **** it bucket.
It will get better if you walk from the business and make cars a hobby...when I did it I realized I didnt enjoy working on minivans and pickup trucks all the time, I just wanted to work on my V8 classic cars...