They voted 4:1 for the alternative retirement and disability plan in 1981. Anyone taking a Galveston County job would be well aware of the personal choice they are making.
The ROI is 3x that of SS and includes life insurance and the accounts are owned by the employees and their families. The life insurance alone would surpass the $40k you mention.
The retirement income for employees with 20 to 40 years of service is calculated to be two to five times the retirement income of Social Security. Disability insurance pays 60% of salary up to $5,000 per month and life insurance is three times annual salary up to $50,000 per year, i.e., a total of $150,000.
They could have doubled the benefits if they opted for stock market-401k type stragety but they went with more stable, like survived the Great Depression stable, insurance (whole life I bet) strategy and still came out way ahead of SS.