الْجَهْلُ كَالْمَوْتِ.
Ignorance resembles death.
The point is not to paint a picture of bodily death but to associate ignorance with deprivation and lack of effective life. The relevant meaning is grasped intellectually rather than as one particular sensed object.
Classification follows the sense intended in the comparison, not every possible use of a word. Death is also a bodily event, but here it functions as an intellectual comparison with ignorance.