They have much to lose because e-cigs are not used for tobacco, in my experience.
So they (tobacco corps) will lose future tobacco addicts to e-cigs and vaping liquid producers.
Tobacco is an industry with high regulatory barriers to entry and decades of very effective marketing behind it. "Big Tobacco" makes money at the wholesale and retail levels pretty much unopposed.
Vaping is effectively unregulated, and there really aren't any truly big players in e-liquid market. Everyone who vapes seems to have their favorites, but even a small vape shop will have a dozen or more brands on the shelves.
Vaping isn't going to kill tobacco use, because as you said, the nicotine ultimately comes from tobacco - but its rise is cutting significantly into the revenue of "Big Tobacco".