Unable to Create 'Export to Smartlead' Column - Error Explained

Hi team! Could you help me figure out why I cannot create an 'Export to Smartlead' column? I see an error 'This table is limited to 70 columns', however I have only 51 columns currently https://app.clay.com/workspaces/265671/tables/t_bBnYDMm7oGC2/views/gv_WDWJxd2cWkMM