Sorry for the problem with the WordPress installation. Check out this screenshot:
Softaculous wordpress install
This was installed on my test server. If you leave the "in directory setting" blank, then it will install directly to the web root (public_html). If you put a folder name in that space, then the subfolder name will be created based on your entry.
Also, by our terminology, you're not purchasing "subdomains", you are either registering a domain name or purchasing a hosting account that can hold the files for you website. Domain names can be used as the primary domain, an add-on domain, or as a parked domain on a hosting account.
A subdomain looks like this:
subdomain.main_domainname.com or domainname.com/subdomain
On shared accounts, add-on domains can have their folders saved under the primary domain name's root folder (by default, this is public_html). So, by default, the add-on domains added to the public_html folder can be considered as subdomains to the primary domain. However, the hosting servers know that the domain name is handled a stand-alone domain name if you use it in a web browser. The folder is also accessible through the subdomain structure, but this normally NOT used.
However, you do need to follow this convention, you can always set the root folder for an add-on domain outside of the public_html folder. Many people do this in order to keep the files for the different domains hosted under one account in one place making it easy to organize.
I hope this helps to explain the differences, and how we installed WordPress to the root instead of a subfolder. If you have any further comments or questions, please let us know.