Shulkers, and shulker shells are not affected by the looting enchantment. What this means is you get a pathetic amount of shulker shells from killing them, and someone with looting 3 will get the same amount of shells as someone punching them to death with a potato.

This is very easy to reproduce:
Go to the end void in creative, spawn 10 shulkers on magma blocks, then go and kill 10 shulkers using looting 3. You will see that the ones on magma blocks drop more or less the exact same amount of shells. And that you also never get 2 shells from killing a shulker with looting.

Take this to the extreme and get a looting 255 sword, repeat the above steps, and no addition shells will be dropped.

There are many, many, many more problems with the loot tables on bedrock, but i don't have the time to search for all the bug reports, or make them if they do not exist. If anyone is interested, here is a video i made on this topic 💖 https://youtu.be/83lHypE6bfk