The YouTube recommendation system is optimized to direct all users toward pools of content that have the highest amount of watch time. The AI has learned about various paths that get users to watch for longer amounts of time. One of those paths is right-wing polemics. Another path is, say, makeup tutorials. It's not inherently political.

Purely by its own machine learning, the YouTube algorithm becomes sophisticated at inching people toward the high-watchtime material. There is no mal intent. There's no intent at all except for revenue. The AI doesn't "know" what the content of the reactionary videos even is. All it "knows" is that people who get there watch longer, and that people get there by way of other interests, such as martial arts, history, or guns. It also "knows" that this transition has to happen gradually to succeed. The recommendation progression is subtle:

Martial arts -> combat -> guns/militaria -> liberals are coming to seize your guns

Martial arts -> combat -> guns/militaria -> look at this neat Nazi gun -> were the Nazis so wrong???

Martial arts -> MMA -> Joe Rogan -> Jordan Peterson -> feminism is destroying Western civilization

Martial arts -> MMA -> Joe Rogan -> (((George Soros))) is a space reptile

Your line of questioning assumes that this process is malfunctioning, when in fact it is working as intended. You're correct that it's ethically grotesque, but since when have companies ever taken responsibility for externalities without being compelled to via regulation? YouTube has the legal right to host and broadcast whatever (non-obscene, non-copyrighted) content makes it the most money. The only free-market answer would be advertisers pulling money, which they occasionally do as a disciplinary mechanism. But if the advertisers don't really care, well...