I think the much more likely explanation is that 4chan always existed as a genuine counterculture (which was particularly true in the age prior to the late 2010s, when the internet was like a completely different world to real life), and reflected the rejection and inversion of certain societal mores. The rise of a far right current in 4chan exactly mirrored the kind of progressive fundamentalism that emerged in the dominant culture from around 2013. The outer zeitgeist started to abandon a 30-50-year term of post-racial thought, and immutable characteristics like race and gender started to become meaningful as tangible social capital in a kind of "official" way, as ideas like the progressive stack filtered from online circles and Occupy Wall St, through academia, into the halls of power and governments. The emerging racial consciousness of places like 4chan were a direct (and predictable) reaction to that.

The reason that places like 4chan became a far-right haven and other areas of the internet didn't has nothing to do with whether people tried to raid Stormfront in the 2000s, but is purely a matter of the firm-handedness (or lack thereof) of their respective moderation. Prior to the 2010s, many less-moderated areas of the internet had a variety of political persuasions, but from 2015 to the present day, there is a very strong correlation between the prevailing political leaning of a space and that space's ideological moderation strength.