I don't understand how watching people make faces at things has become a core pillar of media.
There are a lot of factors but here are three big ones:
Lack of companionship
Lack of friendship
Lack of both of the above causing one to watch a reaction vid to emulate the feeling of watching something with a friend.
Covid helped push this forward and made people more introverted, which had a bit of a cause and effect to it that helped reaction content become more viewed, especially as people tuned in to more viral moments.
Content companies and ad companies still can’t figure out how to interact with this form of react media.