The reason is, the Injured Spouse form ( Form 8379) will not be available to e-file or print until March 17, 2022.  Once the form has been approved by the IRS, you can then file.  

IRS forms availability table for TurboTax individual (personal) tax products

https://ttlc.intuit.com/community/forms/help/irs-forms-availability-table-for-turbotax-individual-pe...