I am just taking a VERY WILD guess. It takes some time to train programmers into how the tax forms work. They don't need to know the tax law, but they gotta know how the tax forms work so they know what numbers to send over to what documents and how to add it all up. I am guessing they decided it wasn't worth their time to train programmers in how to work the Form 8997 and make it flow to Form 8949. They probably analyzed their customer data and found that people who have this level of investments most likely do not use TurboTax or the few that would was not worth it for them to train programmers.
Just a wild guess.
