I understand but can list a few potential reasons:
- the system keeps all the power for the essential things you talked about, limiting the performance of things like the browser
- It runs on an Intel Atom which is a low power chip
- A web browser is a surprisingly complex piece of software that is in constant change. The software team at Tesla don't see the browser as a priority so it doesn't get enough attention to be optimized.
The good news is that new cars come with an AMD Ryzen chip which is much faster. The browser probably runs better on those.