Because thats how they control the population. The left used to mean the people who supported state owned unionized industries that provided good secure jobs with good pay and conditions for the working people. They were the antithesis of the globabalist corporate enslavement of the working people to the Wallstreet overlords see all across the world today.

That old working class left was a direct and very real political threat to rule by the corporate elites so they infiltrated their movement it and took control of it. They pushed out everyone who supported the old left ideology and replaced it with the ridiculous race and gender based parody we see today. That is why today, there is no political opposition to working class enslavement by the globalist elites.