Not to advocate for doing either, just to point out potential flaws in your argument:
(1) Value gained
Assuming you steal things that aren't of high value, let's say you steal a bag full of groceries at the supermarket, every day, worth $50. Do this for a year, and you'll have stolen < $20k of goods.
Assuming an annual salary of $100k, if you slack off 75% of your working hours, you'd gain a "windfall" of ~$75k.
Conclusion - the payoff for slacking off is much higher.
(2) Risks and adverse outcomes
Shoplifting is a crime in most jurisdictions. If you get caught, you'll have to deal with law enforcement, even if you don't get prosecuted in the end. That's generally quite unpleasant. If you are prosecuted and found guilty, it tends to make your life quite a bit harder given that many employers are opinionated about hiring people with a criminal record. Not to mention fines or even prison.
If you slack off at work, the worst thing that can happen is a confrontation with your manager, your coworkers look at you funny, and you get fired from the job. This is almost strictly worse than the adverse outcome for shoplifting because if you get convicted of shoplifting there's a good chance you'd lose your job anyway.
Conclusion - the risks and adverse outcomes of shoplifting is much worse.
So in summary, it can be rational to slack off at work but not shoplift for purely selfish reasons.