Users are prompted to hit the 'Get Nitro' button to begin the link process.
When you link your Steam account to third-party services, a pop-up window appears explaining what you're linking and that you should be aware of scams. However, a pop-up doesn't appear when you select the Get Nitro button on the phishing page. The page still changes to mimic the Steam third-party account link page, but it's built into the original phishing site rather than accessing the Steam service. The attackers want you to enter your Steam account credentials on their site, which they'll hoover up.