Because I've studied metaphysics? It's not even a quirky feature of abstract objects it's often how they are defined. Now that distinction may be merely an indexical one-- the physical universe could be an abstraction in some other physical universe and we just call ours 'concrete' because we're in it. But the distinction is still true.

If you can give an instance of an abstract object exerting causal influence that would be big news in metaphysics.

(Note that an abstract object exerting causal influence is not the same as tokens of that abstraction exerting causal influence due features that the token possesses in virtue of being a token of that abstract object. That is "Bayes Theorem caused me to realize a lot of my beliefs were wrong" is referring to the copy of Bayes Theorem in your brain, not the Platonic entity. There are also type-causal statements like "Smoking causes cancer" but these are not claims of abstract objects having causal influence just abstractions on individual, token instances of causality. None of this, or my assent to lessdazed question, reflects a disparaging attitude toward abstract objects. You can't talk about the world without them. They're just not what causes are made of.)