Direct link to blog address oddity

This is more curious than a problem, but I was hoping someone could explain what’s happening…

Under my main web site:

https://www.spinland.biz

I have a sub-directory called spinrants where my WordPress blog is installed. That is also registered as a sub-domain. Normal access to the blog via:

https://spinrants.spinland.biz

works just fine, but if I try to use a more direct URL, such as:

https://www.spinland.biz/spinrants

I get a blog-themed 404 error. Likewise if I try to get even more specific:

https://www.spinland.biz/spinrants/index.php

This came up when in a web page in the https://www.spinland.biz root I tried to make a local link to the blog of simply “./spinrants/index.php” and it wouldn’t work.

Is there a local, direct link that would work? Why does it behave like this?

Many thanks in advance.