Because you did not enter it in the proper place. The form is a SSA-1099, it is not a 1099-R or a W-2 and you do not enter is as such. If you enter it as a 1099-R or a W-2 then all of it will be taxable. To enter the SSA-1099 in the proper place, type SSA-1099 into the search box, click Find then click Jump to.
