They push it because it’s an easy win. Corporations will subvert any cause that doesn’t have directly to do with overthrowing capitalism. They do the same thing with environmentalism and diversity initiatives. That doesn’t mean that those things are inherently bad or part of some sort of secret plot.
From my understanding, the application of the word “gulag” to a prison is to indicate there is strenuous forced labor in harsh conditions in a distant location free from public scrutiny. The implication is that people die from being overworked or due to exposure and the government is able to cover up these deaths because of the remoteness of these facilities. Likely, this implication is meant to harken back to the labor camps of Nazi Germany.
This is irrespective of whether or not Soviet labor camps should be characterized this way or whether US prisons are inherently more humane. If anything, I highly advocate for referring to US prisons by a more pejorative name to indicate their cruel nature. I would use the term “gulag”, but I think what makes US prisons cruel is different from a labor camp and deserves a different name.