Because they have to shrink down to the quantum realm and come back. It uses more. It’s also never made clear how many particles are in the vials or if they’re full or how many a normal shrinking takes. But it is established multiple times that they have a limited supply and only enough to the job. Also, it’s a comic book movie.
Than you, I was going to say modern apples have a taste and texture nothing like apples when this name was created.