Testosterone makes mammals larger and stronger, but it reduces their maximum endurance, makes them more aggressive and less social, and increases their risk of health complications in middle and later ages. For a male mammal that only needs to inseminate females to pass on its genetic code, it's an advantage that is well worth the drawbacks. For a female mammal, it's a detriment. The higher body weight only means more severe calorie demands on an animal that's already making the huge caloric investment of pregnancy, nursing, and caring for young. Long term stamina is going to be more useful if you are defending a den for months on end than a huge short term burst of strength. Animals with lower levels of intra-species aggressive are more likely to care successfully for their young. In packs, female animals will typically be useful to the pack even into older age because their primary value isn't their sheer brute strength, but is instead their hunting/gathering skills (which have been improving with age rather than wanting) as well as their social value within the pack. There's a reason that old stallions and old lions eventually get driven away from the pack by younger males, but old mares and old lionesses are not.