Why the cells of sclerenchyma and tracheids become dead?

Explanation

(i) Sclerenchyma and tracheids are cells which have nucleus initially but it soon degenerates. They become dead cells.
(ii)Sclerenchyma functions to give mechanical strength to the plant. Tracheids are a part of xylem and help to conduct water.
(iii)They have functions inspite of being dead cells.