I suspect forced login then allows the scraping of data from your browser, cookies and such. And links your data with the email given to glp.

Then you can use or sell the data record to others for marketing, research, etc. or simply do your own research on what your visitors look like, what other sites they visit, etc.

I used to be a web admin for a small company and that’s one of the reasons we tried to urge people to login- it lets you do all that data stuff.