Why is it www.google.com and not google.com.www? And if www.google.com is okay, what's wrong with www.google/stuff. Left to right order.
you know there's an actual reason for this?
com > google > www
"www" is a subdomain of "google" which is a subdomain of the top level domain "com"
historically that was a conventional way to separate services (ftp.google.com, www.google.com gopher.google.com)
But actually 'web' reveals to the graph of hyperlinks between http/html pages that let you navigate from page to page, server to server. www denotes the host is primarily a http server serving web pages.
You could argue it's superfluous these days - if you are typing it in an address bar, you hope it is a http server, and if you are typing it in a ssh prompt, you know it's your ssh server. People add it because it's a convention and some users might get confused if you don't... (it's probably a vhost anyway most of the time)
com. only serves the nameserver (NS) addresses for example.com., and if they are within the same domain, their IP addresses. It does not serve the rest of the records for example.com.
You can see this easily with e.g.:
dig -t any google.com. @a.gtld-servers.net.
vs.
dig -t any google.com. @ns1.google.com.
There is no real advantage of having it be 'www' coming from DNS...
There is a somewhat more modern problem which is that having a domain be a CNAME (the DNS equivalent of a by-name redirect) means it can't also have MX records and receive mail; the CNAME also ends up "redirecting" everything, including MX lookups. So if your web host offers yourdomain.someawesomehost.com and you decide to point yourdomain.com to it via CNAME, having you@yourdomain.com doesn't work unless yourdomain.someawesomehost.com is configured to receive mail for yourdomain.com.
google.com.www is in neither ascending or descending order.
www.google/stuff works now that we have generic TLDs and .google is a TLD, but before that it ignores the possibility of google.net and google.org. This may not be a problem for a unique trademark like google but not all domains are trademarks.