It is because an electric vehicle needs to move its own batteries as part of itself (obviously), but you also need more batteries to provide competitive driving

It is because an electric vehicle needs to move its own batteries as part of itself (obviously), but you also need more batteries to provide competitive driving range/power because the energy density is so low. Thus, you need to install more batteries to compensate for the increased workloads that a truck would forseeably experience, but you need more batteries to convey those batteries which requires bigger motors which requires more batteries and herein lies the Tyranny of the Rocket Equation. At some point you need a breakthrough in energy efficiency or energy storage density because you hit an upper practical limit on how much energy storage you can haul around. ICE cars and trucks must also technically contend with this, but in practice they do not because fossil fuels are so energy dense that we almost never meet that upper practical limit.