You pose an interesting question and I might not have sufficient information to give you a full picture, but I might try to show a glimpse of what I think may be happening.

Someone somewhere decided it may be a good idea to expand existing framework ( hate crimes[1] ), which was relatively easily adopted in America due to historical ( slavery ) and political factors ( combating racism ).

[1] https://www.justice.gov/hatecrimes/laws-and-policies

With that in mind, the first step is saturating the media with opinions indicating some sort of support for a policy/law change ( in this case hate speech - links with sample articles follow - note how old some of those are ):

https://www.washingtonpost.com/opinions/2019/10/29/why-ameri...

https://newint.org/sections/argument/2012/12/01/is-hate-spee...

https://www.ihrb.org/news-events/press-centre/the-challenge-...

https://theconversation.com/the-idolization-of-free-speech-i...

Once the population is sufficiently primed, one can run it through congress. It is not a weekend project.

Note that it is exactly the same pattern with encryption battles, but at least that one has clear originators ( usually three letter agencies ).