Doesn't answer the "why" question.
Given that the extended deadline for filing 2020 returns was just a month ago, it seems strange that they have already shut down amended return e-filings. I guess once they have your money they are no longer interested in actually supporting their customers. My 2019 paper amended return (necessitated by a TurboTax bug in the first place) submitted in June still hasn't been processed and I am continuing to wait for my $900. Time to research other tax software providers. Tax year 2021 might be the year when I am finally going to make the switch...
