For me, reusing widely used code that's heavily tested is preferable to the liability of handwritten code. If I'm given the opportunity, when possible, I'm going to choose the former.
That's a good default to start with, but that's not the whole story.
Every system has its own sets of constraints, and its own sets of goals. Those constraints and goals don't necessarily align with the assumptions made in the library you're using, because it's rare to have a library that does precisely what you need.
When you can't find a library that meets your needs, you have two choices: 1) roll your own solution, or 2) find a library that does something similar to what you want, and coerce the library into a form that suits your needs.
Neither are pleasant options, but I find #1 tends to give a better outcome in the long run. You know what your system constraints are, so you're in a better position to design around them.
I feel like the problem comes down to people not willing to read the docs. Reading the freaking manual helps understand if your tools are precise enough or configurable to solve your problems. Then reading the source code (if possible).
Then, assuming it’s still not worth extending, inventing it yourself isn’t such a bad idea.
On the other hand time required to read and _understand_ the source can be often very compareable to writing specific solution to your problem. Which all comes down to one biggest bottle neck of our industry: sharing understanding of solutions.
It needs to be a deliberate decision based on use cases. Depending on your business, it may be more valuable not to relinquish control of important functionality to third parties.
I suppose nobody really invents anything in-house in one sense. You reuse the hardware, the OS, the drivers, the network, cloud storage, IDE, source-control, JIRA, a programming language, several libraries, databases, at least one framework, and on top of all that you may have some sprinkles that are "your application."
I think the question is always, how smart an engineer can you be to reuse the maximal amount possible to deliver a good experience quickly.
Every system has its own sets of constraints, and its own sets of goals. Those constraints and goals don't necessarily align with the assumptions made in the library you're using, because it's rare to have a library that does precisely what you need.
When you can't find a library that meets your needs, you have two choices: 1) roll your own solution, or 2) find a library that does something similar to what you want, and coerce the library into a form that suits your needs.
Neither are pleasant options, but I find #1 tends to give a better outcome in the long run. You know what your system constraints are, so you're in a better position to design around them.