IME those who write code instead of using a dependency are those who DON'T seem to care about quality. They can't be bothered to see if the problem is already solved. They can't be bothered to design a good interface and extract the code into a re-usable module. Just just solve their own immediate problem, which then gets re-solved in different ways a dozen times in different projects in the company. This is what I find frustrating and what I find 3rd party dependencies protect against. They define a set of culturally accepted/known APIs/Functionality that is consistent and doesn't have to be relearned between repositories.
In my experience, I have seen some Jurassic-scale disasters, because of poor dependency choices.
I think a lot of people just google for dependencies, and then add the first one that has a slick Web site, without thinking much about the code they are adding.
I am not a "never dependency" person, but I am anal about quality. Totally obsessed. I feel that quality is something that many, many programmers eschew, in favor of bling and buzzwords.
For me, I won't put my seal on something until I have tested it six ways to Sunday. In some cases, it may be unit tests, but, more often, it is a test harness, which can be a much more ambitious project than a few XCTests[0]. In fact, I am running into a lot of folks that don't know what a test harness is; which is jaw-dropping.
Since I do a lot of device control stuff, unit tests are not particularly useful. In order to create unit tests that would be effective, I'd need to design a huge mock, and that would not be worth it; likely introducing more problems than it solves.
An example is that I am currently developing a cross [Apple] platform Bluetooth LE Central abstraction driver[1]. This needs to have test harnesses in all the target systems (iOS/iPadOS, MacOS, WatchOS and TVOS). I actually have it driving a released app[2] (which is really just a "productized" implementation of the iOS test harness), but I do not consider the module ready for release, as I have not completed all of the test harnesses. I am in the middle of the WatchOS harness now. I may "productize" the MacOS test harness. My test harnesses are really serious bits of code. Complete, ready-to-ship apps, for the most part. Going from a test harness to a shipping app isn't a big deal.
IME those who write code instead of using a dependency are those who DON'T seem to care about quality. They can't be bothered to see if the problem is already solved. They can't be bothered to design a good interface and extract the code into a re-usable module. Just just solve their own immediate problem, which then gets re-solved in different ways a dozen times in different projects in the company. This is what I find frustrating and what I find 3rd party dependencies protect against. They define a set of culturally accepted/known APIs/Functionality that is consistent and doesn't have to be relearned between repositories.