Why do the system apps show 0B memory space occupied?

I had noticed in my phone's applications manager, that the size of the system apps are displayed as 0B, which indicates that no memory space is occupied by that particular app. Please see this screenshot in which the pre-installed Browser app is shown to have occupied no memory space: " class="img-fluid rounded" style="max-width: 100%; height: auto; margin: 10px 0;" loading="lazy"> But, I know that every app is composed of several files, so no app can have 0B size. But, the size of third-party apps are shown correctly. Why does this happen ?