I’m assuming actual researchers know better but Scihub is accessible in plenty of ways. Retracted papers could be shared as a means of spreading misinformation or simply just stumbled upon by regular folks looking up something specific.

Having access to retracted papers is nice but:

Unfortunately, it appears that once Sci-Hub has a copy of a paper, it doesn’t necessarily have the ability to ensure it’s kept up to date. Based on a scan of its content done by researchers from India, about 85 percent of the invalid papers they checked had no indication that the paper had been retracted.