Here's why:

* Chloroplasts are the sites of photosynthesis. This process uses sunlight, water, and carbon dioxide to produce energy (sugars) for the plant.

* Not all plant cells need to photosynthesize. For example, root cells are underground and don't receive sunlight. They instead rely on sugars transported from the leaves where photosynthesis occurs.

* Other specialized cells, like those in the stems or flowers, may have a reduced number of chloroplasts or none at all. They have different functions and don't require the same level of photosynthetic activity.

Therefore, only plant cells that actively photosynthesize, like those in leaves, will contain chloroplasts.