1. Social security theoretically scales with one's income. The portion of income above the 112k limit will receive no SS benefit, therefore not subject to SS tax. People earning more than 112k are still subject to SS tax for the portion of income below 112k.
2. Certain income like your stock trading profit is not subject to SS tax at all because that's not considered earned income and will not receive SS benefit. You are actually enjoying the 0% SS tax treatment. If you are a real person, had real net trading income over any given tax year and filed tax accordingly, you'd know.