Because most of the issues with crosswind limits are the limitation of the pilot, not the aircraft. Not always true, but more often than not. Increasing the stated figures in a manual does not give the pilot better handling skills, just more opportunity to get into trouble.
Note that the max demonstrated crosswind given in some manuals relates to the maximum demonstrated by a skilled test pilot who will have exceptional handling skills. It could be argued that these skills may be somewhat offset by what might be very few hours on type. This is more true for funky unusual types rather than the tried and tested trainers such as PA28s and C150/152 types.
In some cases crosswind limits are hard and can be quite low for demonstrable aerodynamic reasons, such as airframe blanking, or control authority, or for physical reasons such as undercarriage resilience to side load.
Whatever the case a) the limits (recommended, demonstrated, or fixed) are there for a good reason and b) your limits may not be the same as those listed, both above and below. But know which limit you're working to, and don't exceed the wrong one...
Just in my opinion, of course.