But this is precisely my question: in what way does splitting the code into many small files help with that? Personally I find jumping between many files (especially when they are located in various directories on various levels in the fs) pretty annoying...
Of course, that probably depends on the nature of the project. Having all backend code of a web app in one file and all the frontend code in another would be very inconvenient. OTOH, I have no problems with having e.g. multiple React components in one file...
Obviously you can split your code into many files in a way that obfuscates the workings of the program pretty much comoletely. And I think you can write a single 10kloc file that is so well organized that it is easy to read. I just never have seen one...
I believe that files offer one useful level of compartmentalizing code that makes other people easier to understand what is going on by just looking at the file structure before opening a single file. The other guy can't grep anything before they have opened at least one file and found some interesting function/variable.
Of course, that probably depends on the nature of the project. Having all backend code of a web app in one file and all the frontend code in another would be very inconvenient. OTOH, I have no problems with having e.g. multiple React components in one file...