The meristematic cells divide frequently and they give rise to new cells.
For this they require a dense cytoplasm and thin cell wall.
Vacuoles if present will cause hinderance in cell division as it is full of cell sap to provide turgidity as well as rigidity to the cell.
Another reason is that the main function of vacoules is to store nutrients , excess salts etc… and meristamatic cells do not need to store these nutrients because of their compact shape.