Missing context is - there is always something else you work on like the guy was making Eleventy so it was waste of his time.

If you work for a company and build todo app most likely it will not be beneficial for you to implement in-house library because there will be stuff that will bring much more value.

Like you don't have now 2 years to cover for all hard stuff because you have to make synchronization of tasks between devices and your boss most likely won't appreciate that.

"Never roll your own cryptography" is always used in context of building another application it is never "don't become a cryptography specialist".