Probably because EV trucks would need to go through the current Brenner motorway, that is a very trafficked road, from Wikipedia ( https://en.wikipedia.org/wiki/Brenner_Pass#Motorway ):

The ever-increasing freight and leisure traffic, however, has been causing long traffic jams at busy times even without border enforcements. The Brenner Pass is the only major mountain pass within the area; other nearby alternatives are footpaths across higher mountains at an altitude of above 2,000 metres (6,600 feet). As a result, air and noise pollution have generated heavy debate in regional and European politics. As of 2004, about 1.8 million trucks crossed the Europa Bridge per year.