They aren't counted because basically they're forced savings. Typically everything you put into SS you'll get back. Lower income folks end up getting more back than they put in. And the same for Medicare. It's a forced insurance payment of sorts.
The vast majority of the US debt is owed to SS recipients.
And given that the total trust fund appears to be $2.8T, I'm not sure how it could hold the majority of the debt: https://ycharts.com/indicators/us_oldage_and_survivors_insur...
[1] https://www.thebalance.com/who-owns-the-u-s-national-debt-33...
I think to correctly frame what proportion any income group (or wealth group) pays, you have to look not just as federal income taxes, but at all taxes.
More to the point, and I think we agree here, the deception is by framing the discussion only about the "us federal income tax" when that is only 60% of the total federal income/payroll taxes collected. If you tell people that the top 1% makes 22% of the money and pays 40% of federal income taxes it makes them sound oppressed. If you tell people that the top 1% makes 22% of the money, has 35% of wealth and pays 25% of federal income and payroll taxes, the oppression disappears.