Ask HN: Why isn't Social Security more automated?

Every couple of months, a retired person that I know has to spend a significant amount of time correcting ridiculous mistakes that the SSA makes in paying benefits. One month, they suddenly "forget" to count their spousal SSI, and pay too much. Another month, they double-count some SS income as other income, and pay too little. There seems to be no end to the number of ways they can miscount things or simply use wrong figures, which my friend then has to correct by a laborious process of collecting documentation. This has been going on several times per year, for the 5 years since they retired.

I always respond with incredulity. It's just hard for me to believe that a 3 trillion dollar fund could be administered in such a way that individual government employees are free to make numerous mistakes, on a case by case basis for every individual person receiving benefits.

How on earth is a fund this large, with so many transactions, not administered by a computer system that can accurately remember people's situations, and carry out the rules in a consistent manner?