Development usually involves tasks that range from the easy and mundane to the difficult and arcane. And those tasks are usually not simply assigned to a single engineer to either succeed or fail - usually the hard stuff is given to the more advanced coders and the easy stuff is reassigned to whoever can handle it. I can imagine a single coder on a 10 person team who can spend 10 years on a code base doing all the 'easy' parts. There are always tons of maintenance tasks (or 'bookkeeping' bits of work as I like to call it) that are simple, boring, and ever-present up for grabs.
Coding is just like anything else - some people only do the minimum in order to get a "passing grade" and so they never really get past the basics. It isn't so much that they code without knowing how to code, but that whoever is in charge of managing them isn't necessarily an expert on coding and often times people find it easier to improve their ability to trick their manager rather than the difficult task of learning new or more advanced things.
Coding is just like anything else - some people only do the minimum in order to get a "passing grade" and so they never really get past the basics. It isn't so much that they code without knowing how to code, but that whoever is in charge of managing them isn't necessarily an expert on coding and often times people find it easier to improve their ability to trick their manager rather than the difficult task of learning new or more advanced things.