The biggest reason is developer ego. Devs see their code as artwork an extension of themselves, so it's really hard to have critical conversations about small things and they erupt into holy wars. Off hand:

* Formatting

* Style

* Conventions

* Patterns

* Using the latest frameworks or whats en-vogue

I think where I've seen results delivered effectively and consistently is where there is a universal style enforced, which removes the individualism from the codebase. Some devs will not thrive in that environment, but instead it makes the code a means-to-the-end, rather than being-the-end.

As far as I can see in the modern tech industry landscape, virtually everyone has adopted style guides and automatic formatting/linting. Modern languages like Go even bake those decisions into the language itself.

I'd consider managing that stuff essentially table-stakes in big orgs these days. It doesn't stop projects from failing in highly expensive and visible ways.

The UK Post Office lied and made people kill themselves ... because of dev ego?

Ironically, the downvotes pretty much prove this is exactly correct.