It's not about behavioural defects. It's that the _code_ is trash. It is unmaintainable and slows down all future changes, exactly because the person who wrote it didn't take the time to think about the future or even good architecture in the present. Every time I touch their code I have to almost redo their work because:
- It's impossible to understand what is going on (For example when people load huge json or sql files into a single test and you don't know what scenarios it covers because they are too lazy to write dedicated minimal test cases. Another common offense is a not well-defined data model that gets mutated everywhere in dynamic languages like Python or JavaScript where you never know what shape an object has or where it comes from)
- Their code allows so little extensibility that following the same "pragmatism" as they did and just hacking it in would exponentially increase the complexity
- There are no abstraction boundaries which almost surely means insufficient test coverage (which I have to amend before I can even start with my own work so that I don't introduce regressions) or the tests are coupled so closely to implementation details that any change necessary for my own work will require me to rewrite all the existing tests
You are fast because you pawn off your design work to whoever comes after you. Of course you have fewer defects: your colleagues have to put in more time to maintain the same level of correctness or else risk introducing bugs. That's the cost of bad maintainability. It's well known that changing existing code is harder than writing new code, double so if it is not written with care. Someone has to be the janitor to keep the cruft from accumulating and if it's not you, then everyone else has to pick up your slack. Ideally, every person in the team would continually clean up and always leave a code base better than they found it.
Lastly, I want to say that there is very important difference between simple and easy and simple doesn't come for free.