The argument is not between NIH and external deps. The argument is over needless complexity and brittle unreliable bits (which can come through either channel) vs keeping things simple.

In my experience, younger developers will push both (in-house and external) directions at once, actually. Building out complex edifices with sharp corners over a maze of transitive dependencies that few understand.

It's the same thing: A fantasy that a framework will solve the problem, combined with a fantasy that they can develop said framework. It's an urge we all suffer from but some of us have learned the hard way to be careful about. (And others who are great at self-promotion have been rewarded for it by naive investors and managers.)

Finding simple solutions takes humility and time.