Cradle to grave "footprint" is exponentially higher for EV's. But Joe Public doesn't really about their carbon footprint. EV's are considered cheaper to run (whether they are or not is actually still quite debatable, but they are seen as so by the general public). The fact they can can claim that their own personal carbon footprint (which is, at best, what any one individual actually considers) is reduced as a result is merely a justification for saving that £80 periodically, not the (pardon the pun) driving factor.
Or, to putit another way; marketing - buy & run an EV, you, personally, are causing less emissions (just don't consider the bigger picture, please!).