The overwhelmingly vast majority of American transportation gets its power from oil. Anything that could disrupt that - like, say, nuclear power making electricity sufficiently ubiquitous and cheap to make electric vehicles practical - is a threat to the oil industry. Further:

> What had an impact was 'cheap' fracking gas

Which (as the name "fracking gas" would suggest) derives specifically from fracking as a means to extract oil from deposits otherwise inaccessible. That is: gas and oil come from more or less the same place, sold by more or less the same people with the same reasons to want to suppress alternative energy sources like nuclear (and solar, and wind, and geothermal).