When young, the fur often hasn't grown yet. Also, the fur itself may degrade in UV, making it weaker, fading, and losing waterproofing and other properties the

When young, the fur often hasn't grown yet. Also, the fur itself may degrade in UV, making it weaker, fading, and losing waterproofing and other properties the animal relies on. And finally, the cost of fluorescence may be very small - meaning that it may have had some benefit at some point in the past, but there now no selective pressure to get rid of it.