For me I started smoking tobacco back when I used to smoke weed because the nicotine buzz made being stoned all the nicer. Plus there was I guess the rebellious thing that contributed to me starting, my parents hated it and it was yet another thing I could do to piss em off. Then I quit smoking weed and didn't quit smoking tobacco because by that time I was already addicted, but it became an enjoyable way to pass the time, to break up the day with smoke breaks when working, something to do when waiting for a train or a ride, and there is the social aspect of it, as well as being outside all the time when on the road which lends itself to being able to smoke whenever, etc...
However as with any vice, as I've gotten older I've hadda slow my roll, and as of late I've actually stopped smoking tobacco regularly and get my nicotine fix from vaping. Overall I do feel better, lungs don't hurt anymore, I don't get winded, have better endurance, etc... But when on the road I do switch back to smoking tobacco regularly just because it's more convenient vs having yet another device to carry around and charge, or worry about breaking/getting jacked/etc...