They are not going to be able to BS their way through an entire code base.
The problem is that a large number of coders out there simply do not have a project they can show an interviewer. This can be for a number of reasons such as only programming at work or not having much free time. The fact a coder has a project to walk someone through does not imply they are a good coder, so why would a company tailor their interview process to the minority of interview candidates out there who do have a sizable project they can demo?
When I sign up with a company I always get the stipulation that I can use the code for demonstration purposes, that the code will never leave my machine but that I can use it for demonstration purposes. Short of working on some top secret project I would not agree to anything else, not being able to show previous work in this industry is like an artist not being able to show commercial work as their portfolio.
The fact a coder has a project to walk someone through does not imply they are a good coder
No but it is an indication of their work, because it is sitting right there in front of you. Just because they have a project does not mean that it is good, but that is up to the interviewer to decide. If you can look at the code base, then the interviewer should be able to determine if it is well built or not. If they cannot, then I would question whether they should be the one conducting the interview.
so why would a company tailor their interview process to the minority of interview candidates out there who do have a sizable project they can demo
I personally feel that someone looking for a senior developer role should have something that they can demo, they have been in the business for 5 to 10 years, there should be something that they can run on their machine to demonstrate their abilities. Now for a junior developer, I agree they may not have something to demo, but for a junior role I assume a blank slate and look for totally different values. Specifically I look for passion and eagerness to learn, again a test is not going to tell me that.
The problem is that a large number of coders out there simply do not have a project they can show an interviewer. This can be for a number of reasons such as only programming at work or not having much free time. The fact a coder has a project to walk someone through does not imply they are a good coder, so why would a company tailor their interview process to the minority of interview candidates out there who do have a sizable project they can demo?