What is the difference when every problem becomes low-hanging fruit?

OP described a simple 2-line fix that would have been annoying to find by hand. That's a matter of heuristic search. The majority of problems in software engineering do not fall in this category.

More than low hanging fruit, I think it would have been legitimately hard to find. It only triggered 1/512 runs and probably would have required some expertise in crypto algorithms.

BUT regardless, pruning low hanging fruit for any task IS a force multiplier. So much of so many tasks are easy but tedious. Finding libraries, documentation not matching code thus reading code, correct syntax/arguments, and just tons of straightforward tasks which are not HARD but time consuming.