Browsers don't like to route directly to TLDs. In theory, Amazon could have a web site at
amazon
but browsers interpret that as a search request, not a request for a rooted domain name. Even amazon.
which means to treat that as a fully qualified domain name doesn't work in browsers any more.(That's what the trailing "." means. Relative domain names were a thing. If you're on a machine within "bigu.edu", and you want "ourteam.bigu.edu", you can supposedly just use "ourteam" as a domain. This rarely works right, because few clients have domain names any more. Is it even still implemented in most DNS lookup clients?)