Make sure your field names follow the convention of geodatabase. I think you have a space in front of the field names in excel. Try no spacing in front of the field names. Also, follow the convention of geodatabase when loading the data from excel. For example, Field Name would be Field_Name, no reserved words, no spacing in front of the field name and in between two words in the field name.
Glad the solution worked. The space issue seems to have been what the hang up was in my testing. I created a simple table using the same headings that you used and all columns, including "Location", populated in ArcMap. After reading the suggestion on removing a space I went back and added a space in front of "Location". Wen added to ArcMap the column populated with null value.
You have dislike fields, being one is text and one is numerical. Once all fields are set using cell formatting in excel to match attribute table (right click on each attribute field to see if it's "long" "short" "string" ect. and that will clue you in as to how it should be aptly set up in excel) join the table, but try using the "zone" field as that seems to be a field that joined originally without issue. "What" field isn't unique enough for a one to one match.