I always assumed that at the time it was a relatively harder problem, with lower-level languages that are mostly array-focused, no real built-in containers and

I always assumed that at the time it was a relatively harder problem, with lower-level languages that are mostly array-focused, no real built-in containers and no for-each support. This was cured with better programming languages. On the other hand, cache invalidation and naming things are problems that grow harder and harder when systems get more complex, which they obviously did.