Sure, but the point is that there are plenty of questions about oneself that aren't necessarily answerable with only the source code. If I want to know "why am I in a bad mood this morning", I can't answer that simply by examining my genome. Though that's admittedly a bad example, since the genome isn't really like a computer program's source code, so let me try another: if you want to know why a specific neural net failed in some specific discrimination task, it's probably not enough to look at the code that defines how abstract neurons should behave and what the learning rules are like, you also need to examine the actual network - held in memory - that those rules produced.

Of course you might be capable of taking a snapshot of your internal state and then examining that, but that's something quite different from doing a quine. And it means you're not actually examining your current self, but rather a past version of it - something that probably wouldn't matter for most purposes, but it might mattter for some.