>They are not thinking about every single line of code that they write

Honestly for me over-engineering is usually the result of the opposite. Thinking too much when writing and having preconceived ideas about what a codebase ought to look like.

It was Casey from Handmade Hero IIRC who called his style of programming "compression based", effectively just writing code and factoring out what belongs together incrementally. Abstracting things out as they repeat, not consciously by design. I've taken this up more and more as a way to program.