Look at dosage. You can smoke an integer number of cigs a day. I am not aware of anyone smoking 1/3rd of a cig at a time or at least its very unpopular.

I can and do limit my sugar intake but for a treat once in awhile I'll buy one of those extremely expensive yet extremely tasty imported dark chocolate bars and eat one little square as treat per day for a long while. I bet if I ate the whole bar in one sitting I could reignite my sugar cravings, but its just a gram or so of carbs so I'm good.

The counterexamples are I suppose e-cig vape people could just sniff the bottle, or people who drink one unit of soda no matter if its a 6 oz mini can or 64 oz giant cup.

Given the tobacco companies have historically been guilty of pretty much every evil known to mankind I would not be surprised to discover the "unit size cigarette" is at least partially constrained geometrically to maximize addiction, and a smaller or larger dose would result in lower addiction rates.

There might be a maximal addiction dosage of dark chocolate, but non-unit consumption of candy bars is so normal that it might not work as an addiction strategy.