If stripes are advantageous, then why don’t horses and other animals have stripes like zebras do?
Richard Dawkins proposed what is called the ‘Climbing the Mount Improbable”
We can convert the topic to rather generalized one:
If X,Y,Z traits are advantageous, why don’t all the animals have it?
Here is the idea in nutshell:
When a particular characteristic is been developed in any species, it is like climbing mountains (mountain is abstract to evolutionary journey). We all start at the same starting point. There is no question of single best mountain as such. Every mountain is of different height (complexity and nature of characteristic). Some species climb up a particular mountain and stay at the peak. Some other species climbs another taller mountain and stay at their peak. Some other climb a smaller peak and stay there. The characteristic you develop is determined by the mountain peak you are at.
Note: One peak is not bad/less worthy than other peak. They are just different and not comparable.
In this case, the horses have climbed a smaller mount improbable with respect to Camouflage and stayed there. By luck and and probability and chance, Zebras got a higher mountain to climb and hence they have somewhat complicated black-white strips.
We can see this example using eyes. There are 20+ types of eyes in who of animal kingdom. If you see the below diagram, every type of eyes have reached a particular peak and settled down there itself. There is no race to be the best. All you do is by probability climb your mountain and when you reach the peak, settle there. But that time, some of your friendly species may get a chance to climb a higher mountain peaks and stay and some other climb a smaller peak. All is improbable.