If users are only able to save a small number of pictures on the microSD cards before running out of space, it suggests a formatting issue. Improper or incomplete formatting can lead to the card not utilizing its full storage capacity, resulting in significantly less available space for storing pictures. Formatting the microSD cards correctly would ensure the file system on the cards is set up properly, allowing the devices to use the full capacity of the cards for storage. Compatibility, UHD storage capability, and camera storage settings are less likely to be the issue in this scenario.