For every scenario where a shield would’ve saved someone’s life, there’s another scenario where a chorus fruit or slow falling potion or instant health would’ve saved their life as well. The point is most deaths in late-game Minecraft are edge cases, things you can’t really predict or fully prepare for, or if you can, the cost for the most part outweighs the reward. If you tried to be fully prepared for every edge case scenario all the time, half of your inventory would just be full of these random items to save you, and for Youtubers inventory space is very valuable because it reduces the amount of time a project takes since you don’t have to restock as much. The current MC Youtube meta is about constantly trying to one-up your last project so time is a very valuable resource, especially for streamers.

TL;DR: Most deaths in late-game MC are edge cases and most of the time people would prefer their inventory to be full of stuff they use frequently instead of stuff they only use when they’re about to die.