the keyword planer shows in the "normal" configuration similar searches and their search volumns. Added up to our keyword. You have to uncheck this option.
When you search, do you search "keyword"? Likely you will search "keyword" for "xyz". So your site matches "keyword" perfect but does not match for "xzy"!
To search with only one keyword does only make sense by searching a brands Name. EG. an car manufacturer.