I believe I found the issue and think this can be resolved - zombie piglins, and likely all zombies, will not be attracted to turtle eggs if there is not at least half a block of empty space above them to jump on it. In my attempts to reproduce this the mobs were in a space that was only 2 blocks tall, and as soon as I removed the roof or replaced with top-half slabs the behavior works as expected.
I'm observing this in 1.19.11 and 1.19.20, but not consistently. In 1.19.11 I'm seeing it on a realm, and on 1.19.20 I'm able to reproduce in Creative by simply spawning zombie piglins and placing an egg in a flat world and they completely ignore it. I attempted the same repro (creative flat world) on 1.19.11 and it seemed like they were attracted to it, so I'm not sure if something regressed in the 1.19.11->1.19.20 update or if there's a world setting I have inconsistent between the two installs, but it seems like a for sure issue in realms.
I am reproducing this as well. Viewing the map will temporarily restore the name sometimes. Breaking the map out of a frame will reset the name sometimes.
World attached - it's a flat world with FoxyNoTail's Mob Heads pack.
Repro: Spawn some wandering traders and kill them to pick up their custom mob head
Expected Results: Mob heads should be stackable
Actual Results: Mob heads are not stackable.
This was called out as a scenario to keep in tact in the original bug (MCPE-159736), indicating that "there should be an option in the minecraft:wearable component, like "equip_on_use" which by default is set to true and maintains current behavior, but when set to false will act like player heads."
It appears the bug fix did not account for this comment which leads to wearable mob heads no longer being stackable. Given that the game allows for zombie/skeleton/wither skeleton/piglin/creeper/dragon heads to stack, as well as carved pumpkins, there is in-game precedence for stackable headware. Furthermore, custom mob head packs are popular on java via Vanilla Tweaks' 'More Mob Heads,' which is used across several popular creative content including Hermitcraft, so accounting for similar functionality in Bedrock should be a goal and presents an opportunity for UGC marketplace content.