From the interviewer's perspective, how do I know that the code you present as experience is actually yours and not copied and pasted from elsewhere
At least in my case it's trivial to prove it's my code. (Or possibly I'm _really_ good at photoshopping videos of myself and have also spent a ton of time coming up with elaborate answers to every potential question covering tens of thousands of lines of open source code.) But for any sufficiently large project it's not that hard to figure out if the person actually wrote it just by asking a few questions.
There are a lot of people who have actual experience, who can't code.