C# Rigidbody Rotation Resets

I'm trying to create a modified LookAtMouse script that makes a Gameobject with a rigidbody attached move and rotate towards the mouse cursor. However when I try to run rigidbody.MovePosition(targetPoint); the gameobject's rotation resets upon moving the mouse. But as far as I know I'm only moving the rigidbody's position. Any idea how I can fix this so the rotation doesn't reset?

 using UnityEngine;
 using System.Collections;
  
 public class LookAtMouse : MonoBehaviour
 {
  
     // speed is the rate at which the object will rotate
     public float speed;
  
     void FixedUpdate () 
     {
         // Generate a plane that intersects the transform's position with an upwards normal.
         Plane playerPlane = new Plane(Vector3.forward, transform.position);
         
         Vector3 pos = Input.mousePosition;
         pos.y = Input.mousePosition.y-50;
         // Generate a ray from the cursor position
         Ray ray = Camera.main.ScreenPointToRay (pos);
  
         // Determine the point where the cursor ray intersects the plane.
         // This will be the point that the object must look towards to be looking at the mouse.
         // Raycasting to a Plane object only gives us a distance, so we'll have to take the distance,
         //   then find the point along that ray that meets that distance.  This will be the point
         //   to look at.
         float hitdist = 0.0f;
         // If the ray is parallel to the plane, Raycast will return false.
         if (playerPlane.Raycast (ray, out hitdist)) 
         {
             // Get the point along the ray that hits the calculated distance.
             Vector3 targetPoint = ray.GetPoint(hitdist);
  
             // Determine the target rotation.  This is the rotation if the transform looks at the target point.
             Quaternion targetRotation = Quaternion.LookRotation(targetPoint - transform.position);
  
             // Smoothly rotate towards the target point.
             transform.rotation = Quaternion.Slerp(transform.rotation, targetRotation, speed * Time.deltaTime);
             
             rigidbody.MovePosition(targetPoint);
         }
     }
 }