No health shown when riding custom Entity {Please Remove}

When creating a custom entity that the player can ride the entity's health is not displayed while it is being ridden like you get with horses. I suspect that this is maybe hard coded to vanilla entities only.

The custom entity contained the following Components:
interact
type_family
collision_box
damage_sensor
movement
movement.basic
navigation.walk
jump.static
push_through
fire_immune
input_ground_controlled
physics
inventory
equipable
timer
fall_damage
environment_sensor
health

If I change the identifier in the custom entity's description from it's custom identifier to minecraft:horse I am able to see it's health from the heath component.