I can´t tell you why ccp did not implement links directly to all the subsections of the webpage. But the use of subdomains in itself is not really an exotic practice. It´s rather quite the norm for big websites.
edit: Using subdomains has one very big advantage compared to not using them.
Now this is just a theoretical example.
Lets image ccp would have the following structure on their webserver:
They have a main folder in which you find the index.html file which is linked to the domain https://www.eveonline.com/
In that folder they have several other folders which contain the pages for different subsections.
For example there could be a folder named community…
Technically it would be possible to access this folder or pages in the folder using the address
https://www.eveonline.com/community/main.html which would display the main community page.
While still being easy enough to access… "https://www.community.eveonline.com/ " is used as the subdomain to directly access that community main page, which is a bit easier to remember for users.
Now we can take this even further, if the community folder has another folder inside which is named “forums” which again contains a file named “forumsmain.html” to directly access the forums through that you would have to type in: “https://www.eveonline.com/community/forums/forumsmain.html” (or more likely .php or whatever but let´s just stick with .html to keep it simple ).
With the use of the subdomain you shorten it to http://forums.eveonline.com which is a lot shorter and more user friendy.
I guess I can stop at this point, but I hope this makes clear how messy web addresses can become without the use of subdomains, directly pointing at the relevant pages :).