Why does intaglio printing require high pressure?

In intaglio printing, high pressure is required because the process involves more than just transferring ink from a flat surface; it is essentially a method of embossing the paper into the incised lines of the plate.12

Because the ink is held within grooves or incisions below the surface of the plate, significant force—often several tons—is necessary to push the dampened printing paper deep into these crevices. To achieve this, the inked plate and paper are passed through a roller press between two rollers, typically with layers of printing felts draped over them to ensure the pressure is distributed evenly. This intense pressure forces the paper into contact with the ink, effectively pulling the ink out of the recesses and transferring the image onto the paper.123