So you should really consider to just ask a question if you have a problem with your site or setup instead of complaining thats its illogical
The first was shadowing the second.
Apache is showing the first website if there is no matching domain in the apache configuration.
If you create a website with domain: domain.tld, then you will be able to access thsi site in the browser when you enter http://domain.tld
in the web browser. If you enter www.domain.tld
in the browser, you will not get this site of course, as www.domain.tld
is not listed in the setup. You then have several options:
a) select auto subdomain "www" in the site settings.
b) add a subdomain "www" for this site.
c) add a aliasdomain www.domain.tld
to this site.
d) select * as auto subdomain. But this will match all subdomains and redirect them to the site, so this setting is only a good choice if you e.g. run a cms system like wordpress MU, where users can get their custom subdomains and use this in conjuction with a wildcard DNS record.
Another example, this time when auto subdomain "none" is used. I have a customer which runs several internationalized sites on subdomains. For example us.domain.tld and de.domain.tld. In this case, you enter "us.domain.tld" in the domain field and set auto subdomain to none. So if someone enters us.domain.tld in the browser, he gets the content of this website.