There are a couple of possibilities.
First, your long term care premiums can be limited based on your age bracket, so the medical expense could be less than you expected.
Second, any HSA distributions that you made are automatically subtracted from what you entered in Medical Expenses. It's a common oversight to add HSA expenses in the HSA interview, and to forget to add the original bills in the Medical Expenses section (failure to do so reduces the apparent amount of medical expenses).
