reason for the growth in plants is limited to certain regions ?

The reason for this is the presence of meristematic cells which are present only in some regions in the plant.
Meristematic tissues are cells or group of cells that have the ability to divide. These tissues in a plant consist of small, densely packed cells that can keep dividing to form new cells.
Meristematic tissues is found in the followinglocations:

near tips of roots and stems. This is called apical meristems.
in the buds and nodes of stems.
in the cambium between the xylem and phloem in dicotyledonous trees and shrubs.
under the epidermis of dicotyledonous trees and shrubs (cork cambium).
in the pericycle of roots, producing branch roots.