Gen Z and Gen Alpha are not doing the cowing. If you cow, you intimidate someone else. That is not what is happening in the excerpted sentence.
Rather, they are the intended targets of the cowing, which would require the use of "be," for example:
> Gen Z and Gen Alpha won't be cowed by authority for authority's sake.
Not only did I read the link, I understood it, which seems to have evaded you.
Gen Z and Gen Alpha are not doing the cowing. If you cow, you intimidate someone else. That is not what is happening in the excerpted sentence.
Rather, they are the intended targets of the cowing, which would require the use of "be," for example:
> Gen Z and Gen Alpha won't be cowed by authority for authority's sake.