Well really, this is somewhat conjecture to speak on, but I see it as a list of things. In the West, communism is microscopic, but is allowed to exist in its current fashion because:
- In its current form, proper Marxism-Leninism of the West is impotent, and not threatening to Empire. The West is more concerned with crushing anti-imperialist nations, extracting superprofits, and tightening its loosening grip on the global south.
- It would 'show the empire's hand' to crackdown on Marxist sites that get only a couple thousand views per day, mostly from the same users. For the population of the West to stay subservient, and continue allowing the bourgeoisie to exploit the Earth, they need to believe they're in peaceful freedom-of-speech land and aren't at risk of government crackdown by visiting the wrong site.
- The resources necessary to track and destroy all gatherings of Communism online are more costly that its worth. The internet is not a real place, and nothing that happens on it is real. Crushing every single site registers by a suspected Marxist is a lot more difficult than flooding every website with anticommunist botfarms, manipulating the highest traffic sites to be pro-empire, and using algorithms to discourage communist content. When things get hairy, you crush the movements organizing in real life. If some workers in Indonesia wanna read Capital, let them, it's more of a pain to try and stop them considering there's hundreds of ways they could access it. If they start striking and shutting down factories, send in the blackwater mercs and the problem solves itself.
- Capitalists were overconfident. Many of them are competent enough to be brutal imperialists, but when the USSR fell, many of them felt it was 'the End of History' and that Capitalism had won its final victory. There was no need to crush marxist bookstores or ML YouTubers because their ideology was dead, all that they were now were ways to generate some small amount of capital from views and ad clicks.
All of these reasons are visibly starting to become more trouble than their worth for the bourgeoisie. More nations are passing anti-communist media laws and actively banning leftist speech or artworks, denouncing 'far-left terrorism', and generally taking steps to behead very large online communist gatherings are all things happening right now in the face of the rise of China, which will trigger another Red Scare. During that Red Scare, the tiny Marxist sites you speak of will be deplatformed as soon as possible, and if they aren't they'll be used as honeypots for when someone who visits Marxist Archive gets their PC subpoenaed for evidence in a court case.