Initially the side panel "new view" link proposed to create view from the current context. If you were inside a folder, you had the possibility to create a view directly inside that folder.

But due to the missing "newView" web method inside View (what an irony), there was a bug: if you are inside a view (inside a folder or not), the link brings you to a 404 page.

After the correction of this bug (JENKINS-48447), the other feature (creating a view inside a folder) was broken.

Workaround: You still have the possibility to create a view inside a folder by using the + button in the view tag list in the "main panel".

"re-discovered" during archeology while working on 3633(https://github.com/jenkinsci/jenkins/pull/3633/).