Because static methods cannot be overridden, that is, they do not exhibit polymorphic behaviour.
An abstract method is meant to be provided an implementation by one overridding method in a subtype of the type where it was declared. The abstract method was born to be overriden.
However a static method already has an implementation that is independent of any instance of its class, and of course, independent of instances of subtypes. The implementation of a static method is bound to the type where it was declared. This is the opposite to
polymorphism. The static method was born to be called as it is, without the need to create any instance.