Sometimes they have been either over or under watered by staff who don't care or understand how to take care of plants. Then they usually die within a couple of weeks of purchase. I usually buy plants from this local plant store that expands operations in the summer. It's run by a couple of women (actually sisters) and their plants are always healthy. They're a little more expensive than HD but it's worth it to get good plants.
On the other hand, container gardening on condo balconies can be tricky - wind can be very drying and with the current tendency for balcony enclosures to be mostly solid or glass, you can end up with a heat well when there is insufficient wind - good in the spring, but it can cook your plants in the summer. Another factor is getting the drainage right otherwise your plants can get root rot or conversely, the soil doesn't hold sufficient moisture. Some plants are more tolerant than others.