Some sites rely on multiple domains to work. E.g. open auth, cdns are usually a separate domain, a lot of big corporates create new domains for “microsites” whe

Some sites rely on multiple domains to work. E.g. open auth, cdns are usually a separate domain, a lot of big corporates create new domains for “microsites” when they want to do something new but are tied down by slow moving corporate practices (although the world would be a better place without microsites). Basically, you couldn’t do it without breaking a large part of the internet.