Filed married joint because TTax said to. Later tested married separate and tax bill was lower (higher fed but much lower state). Why does TTax not catch this?

[DanielV01]

Depending on your state, you may have been able to do both.  Some states allow you to file separate returns as spouses, or a "separate-combined" return (both incomes reported and taxed separately but the tax result is combined).  TurboTax may suggest a filing status, but you can ultimately try different methods to get the best result.

And with Married Filing Separate, you want to compare the combined result of you and your spouse, and not just your result, to make sure you are getting the best overall result.