Some attributes are not saved to NBT upon entity spawn (including player respawn)

When a mob spawns (either spawners, naturally or eggs) it is missing the generic.max_health attribute.

To reproduce:

1. Create a new world
2. Find a mob (either monster or peaceful)
3. Run the command (I did this with a sheep)

   /data get entity @e[type=minecraft:sheep,limit=1,sort=nearest] Attributes

1. As you can see only the follow_range and movement_speed attributes are present, max_health is missing.