The problem is when you get 1000s of such resumes, but only a few positions to fill. Also, not everybody has time to spent on github projects. It can be even more time consuming to work on personal projects than brushing up your algorithmic skills. Not saying these interviews are perfect, but I do believe that they are a good solution for a very big company.

Talking about system design interviews, I had the feeling that they were less useful than algorithm interviews, especially for a senior SWE. You can nail them with only theoretical knowledge, even though you've never worked on the systems they ask you to design.