Blind requires you to have a company email in order to even participate, meaning if you left the company, you no longer can sign up for Blind. So if you want to review a company, how would you?
Blind also targets having communities for people inside companies to talk, and facilitating discussion. Glassdoor is mainly about reviewing companies.
A manager on my old company's blind (they never revalidate your email apparently) just posted the other day how the CEO asked the managers 'who in their team would you not hire today'. They took that list and fired all of them.
I imagine HR would absolutely love to take that down.