I think the reason why they did that originally was so HTTP websites would get referrer information from Google search results (HTTPS). Referrer data is dropped

I think the reason why they did that originally was so HTTP websites would get referrer information from Google search results (HTTPS). Referrer data is dropped when going from HTTPS to HTTP. When Google first started using HTTPS, most of the web was unencrypted, and they wouldn't be able to track the referrer in Google Analytics unless they added a redirector to search results.