Because the scenarios in question are only concerned with emissions from transportation, but more importantly disregard storage. Multiple countries at present,

Because the scenarios in question are only concerned with emissions from transportation, but more importantly disregard storage. Multiple countries at present, at times, exceed their energy demand by renewable production...but the excess is pretty much just lost, their isn't adequate storage to bank that energy. EVs do bank that energy, and more importantly they're likely to do it during the parts of the day demand isn't as high (i.e. peak sunshine). Moreover, centralized emissions control or reduction is much more addressable then 1,000,000 individual combustion engines.