Tobacco contains not just nicotine as active ingredient, but also a rapid-acting MAOI (there might be a couple, the name escapes me, you can google it). MAOIs inhibit the enzyme responsible for the breakdown of dopamine in the synapse, so this significantly potentiates the "hit" associated with tobacco products that you don't get with products containing just nicotine, like the gum, patches or vapes. This is why tobacco companies have been artificially raising the levels of MAOIs in their products to make them more addictive without increasing the nicotine (as in most western countries the nicotine level needs to be declared, whereas the MAOI level doesn't, so they can make their cigarettes more addictive without anyone knowing) - by the by, there was a really good film about just this called The Insider, starring Russel Crowe and Al Pacino, and it was really really good.
I found it interesting to find out how they discovered the MAOI in tobacco - it was apparently because researchers were trying to research nicotine addiction, and so used lab rats as is protocol. However, unlike with cocaine, heroin, amphetamine, and every other addictive drug yet used on rats, they couldn't get them to self-administer nicotine. It wasn't until they added an MAOI to the solution where, lo and behold, the rats began pressing their little nicotine buttons. So, the MAOI is essential to the pleasurable, reinforcing and addictive properties of tobacco, and until the alternative products can introduce one, they will never be quite the same as a cigarette. Also, another potential factor that's been suggested is the carbon monoxide providing a small contributing factor, due to slight oxygen deprivation, but it's primarily the MAOI that is the cause of the difference between tobacco and nicotine-containing products.