Whether a problem is "good" or "bad" is not always objective or simple.

For example, you can have problems that are underspecified, with hardcoded tests for a particular solution (out of multiple possible solutions). If your solution works fine but used a different function name than the one hardcoded in the tests, you can unfairly score 0.

When an eval has underspecified problems like these, you can still score 100% if you remember the original solution from your training data or if you just have taste similar to the original human authors. And both of these qualities - good memory and good taste - are great, but they'll be rewarded unfairly relative to a model that still did exactly what it was asked but in a different way than the hardcoded tests expected.