I'm not 100% how to respond to this except that virtually all Americans are enrolled in SS. If you have an SSN, you're enrolled. You need 40 credits at up to 4 credits per year (~ $5500 is required to get all 4 credits). After working about 10 years (even part time) you should qualify for benefits.

According to the SSA, approx 90% of Americans over 65 collect. https://www.ssa.gov/news/press/factsheets/basicfact-alt.pdf

There are still hardships because it's not a full income replacement, but it's a far cry from 'not all are worry-free rich'.

Edit: The majority of the remaining 10% are covered by state level public employee retirement systems who don't accumulate SSA work credits and private pensions. SSI also exists to provide 75% of the poverty line if you have extremely limited means. Here is a paper by the CRS about senior poverty. https://fas.org/sgp/crs/misc/R45791.pdf