1. The First and Last Names could be missing because your report has Business and Family accounts. When adding an account, there are three options under the Name Format drop down; Individual, Business, and Family. Business and Family name formats do not have First and Last name fields. All three name formats do have Account Name and Sort Name. 

2. Your organization hasn't completed the Name Format Conversion. Organizations whose database was created before the 7.16.0 release had a single Name field to enter all information in. With the release came the Name Format Conversion, which is a five step process that allows for Individual Names to be split into two cells in a report, First and Last Name.