How to convince the odschool of programmers that it is better to use components than to write the code yourself?

Question

Frameworks

Actually, subject. We need articles, books, something authoritative that can appeal to people who have worked in banks for 20 years.
Yes, I understand that you can’t get too carried away with frameworks either, but, in this case, there is a huge software project where developers do not trust the system functions for parsing ini files and write their own, not to mention higher-level code. There is even a self-written analog of vsprintf (), its own validators, everything is its own, any attempt to look at third-party components with a narrow specialization is faced with "we don't need it, we'll write it ourselves."
there was no fresh blood in the project for 6 years. The necessary heavy artillery ^W literature on the topic ... I don’t even know how to formulate it.
"Pass system functions to standard libraries and focus on business logic", probably because the product's functions have not moved on for a couple of years.
Thank you!

Answer 1

The question is really subtle.
I do not presume to argue about rewriting system functions, but I personally understand the inadmissibility of using heavy (albeit highly specialized) components.
In banking projects, no one will allow you to use a third-party component taken "because you wanted to." Simply because the cost of a mistake is much more than the salary of all your IT combined for years to come. Therefore, only deeply tested components with known, predictable behavior are used.
Any third-party component is a new potential point of failure, because for your IT it is a black box (no one knows exactly how it works) + for any it will have some amount of functionality that your project does not need. Yes, you can understand how it works, cover it inside and out with tests. But this will take more time than writing the necessary functionality from scratch.

Answer 2

There is one subtle point here,
if everything works well and quickly, then there is no need to change anything for them.