We don't index absolutely everything. Your most recent screenshot is of a setting when editing a forum and it isn't part of the Options system.
In the Options system we generally only "index" the title e.g. "Default image processor", the description e.g. "XenForo can make use of various different image processing libraries to produce image thumbnails etc. Select your preferred library from the list above." and the option ID e.g. "imageLibrary".
I say "index" because it's not exactly an index but a live database lookup which looks up the search query in certain phrase groups, and the option ID.
But, ultimately, this is working as designed. It's just about searching for the right thing.