Both materials build a solid wardrobe, but they solve slightly different problems.
Block board uses solid wood strips as its core, which makes it lighter than plywood of the same thickness and gives it excellent screw-holding strength — useful for large panel doors and shelving that spans a wide gap without sagging.
Plywood, with its cross-layered veneer construction, is generally stronger and more stable across humidity changes, and its face takes laminate or veneer more evenly.
For a tall, wide wardrobe with long unsupported shelves, block board's lighter weight and screw-holding usually wins. For a wardrobe in a humid room, or one that needs a flawless laminate finish, plywood is the safer bet.