Two more to the scientists' tab:

1. No tests of any kind. "I know what the output should look like." Over time people who know what it should look like leave, and then it's untouchable.

2. No regard to the physical limits of hardware. "We can always get more RAM on everyone's laptops, right?". (You wouldn't need to if you just processed the JSONs one at a time, instead of first loading all of them to the memory and then processing them one at a time.)

Also the engineers' tab has a strong smell of junior in it. When you have spent some time maintaining such code, you'll learn not to make that same mess yourself. (You'll overcorrect and make another, novel kind of mess; some iterations are required to get it right.)