I wonder if the writer asked the website that sent their e-mail to TikTok why they were doing that in the first place. To be honest, I'm not sure I understand

I wonder if the writer asked the website that sent their e-mail to TikTok why they were doing that in the first place. To be honest, I'm not sure I understand why would you want to put a tracking pixel from TikTok on your website? What is the gain for the website?