21w05a added the entity killed event. However, the entity hurt event overrides this in most cases, except for killing an armor stand. (It also does not work for boats, items, or minecarts, but the way the code is written makes these specific instances seem intentional)

This can be seen by attaching a comparator to a sculk sensor. Killing most entities gives a power of 8, while it should give a power of 13.

Relates to MC-213668