Social Security Solvent?

Why will the administration nor the president's debt commission, seriously consider removing the cap on Social Security? How is it fair that someone making $80 pay 100% of that salary into the social security fund when a person making $300k only pays 35.6% of that salary into the social security fund? Why can't there be fairness in that if you make $300k a year, you pay the 6.2% on ALL of that instead of just up to $106,800?