Saddles don't apply attribute modifiers when worn by entities

The Bug:

Saddles don't apply attribute modifiers when worn by entities.

Steps to Reproduce:

1. Summon a horse equipped with a saddle that increases movement speed by using the command provided below.

   /summon minecraft:horse ~ ~ ~ {Tame:1b,SaddleItem:{components:{"minecraft:attribute_modifiers":{modifiers:[{amount:1.0d,id:"minecraft:mc-80243",type:"minecraft:movement_speed",operation:"add_value"}]}},count:1,id:"minecraft:saddle"}}

2. Mount the horse, move around, and observe its movement speed.
3. Take note as to whether or not saddles apply attribute modifiers when worn by entities.

Observed Behavior:

Saddles don't apply attribute modifiers when worn by entities.

Expected Behavior:

Saddles would apply attribute modifiers when worn by entities.