A practitioner of physics is known as a physicist. It seems like it would logically follow that a practitioner of metaphysics would be known as a metaphysicist; yet, in every text I've read, a specialist in metaphysics is referred to as a metaphysician. What is the reason for this distinction? 

The OED has an entry for metaphysicist, citing the origin as:

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> Late 19th cent.; earliest use found in The Ladies' Repository. From metaphysic + -ist, after physicist.
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However, its use seems rare.