1099R From Variable Life Policy

This year I cashed out a PrinFlex life insurance policy from Principal.  The Gross Distribution was $170k and change, while the taxable amount was $70k and change.  The gross distribution shows up as income for the year and I am concerned that this will affect my Medicare payments in 2 years (IRMAA).  The non-taxable portion is a partial reimbursement for premiums paid after tax.  Why does it then show up as income?