You need capable engineering for building it yourself. If you only got engineers, who only ever reached for libraries, in ecosystems like NPM or PyPI, you will

You need capable engineering for building it yourself. If you only got engineers, who only ever reached for libraries, in ecosystems like NPM or PyPI, you will find them hard-pressed to develop solutions for many things themselves, especially so, if they are supposed to be solutions, that stand the test of time, and have the flexibility they need. It takes a lot of practice to "avoid programming yourself into a corner". Another thing I noticed is, that one can often easily do better than existing libraries. In one project I implemented a parser for a markdown variant, that has some metadata at the top of the file. Of course I wrote a little grammar, not even a screen of code, and just like that, I had a parser. But I did not expect the badness of the frontend library parsing the same file. That one broke, when you had hyphens in metadata identifiers. At first I was confused, why it could not deal with that. Then it turned out, that it directly used the metadata identifiers as object member names ... Instead of using a simple JSON object, they had knowingly or unknowingly chosen to artificially limit the choice of names and to break things, when there are hyphens like in "something-something". In the end my parser was abandoned, people arguing, that they would have to "maintain" it. Well, it just worked and could easily be adapted for grammar changes. There was nothing difficult to understand about it either, if you had just a little knowledge about parsers. Sounds incredible, but apparently no one except me on the team had written a parser by using a parser generator library before. And like that, there are many other examples.