CA Service Desk 14.1 still uses old Excel (.xls) To export data. This format has many limitations. It can carry only 65000 rows. It is also considered as insecure by Microsoft.
Please update CA Service Desk, so it is capable to export data into modern OpenXML format (.xlsx). It would not only improve user experience regarding number of lines of data but it will also allow use of these exports in environments with strict security rules without nagging dialogs.