Why am I doing wrong?
You’re breaking WordPress. On a subdirectory installation, the /blog permalink is there on purpose and for a very specific reason – to make your main site continue to work while still allowing you a network dashboard.
When you install a subdirectory site, WordPress automatically uses /blog for the main site to prevent collisions. There are ways to not use /blog, though.
- Use a subdomain installation instead (possibly not an option)
- There are plugins that claim to allow you to remove
/blog
Really, it’s there to keep other things from breaking … so by going in and manually removing it, you’re taking things into your own hands and breaking something else.