i dont understand why Observable insists on topological execution. isn't out of order execution one of the biggest complaints about notebooks?

Not exactly. Jupyter notebooks execute top-to-bottom at startup and then you can manually execute cells in whatever order you choose after that. I believe it’s the manual execution that gets people, because it can have inconsistent results. But just rerunning the entire file automatically (like reloading a web page) might be slow if some build steps are slow (they can read or write huge files), and some people have slow steps in their notebooks. They could use manual cell regeneration to intentionally avoid rebuilding cells, when stale data is acceptable.

On the other hand, I don’t know if Observable Notebooks 2.0 even does incremental builds anymore? If not, it’s just about presentation order, similar to literate programming.

Observable Framework had data loaders for creating static snapshots of data at build time. I don’t see any mention of how to handle data loading in Observable Notebooks 2.0.

Why should irrelevant nerd junk be at the top of my notebook? If the point of the notebook is to inform and educate the reader, that's a distracting limitation.

Because it makes the reactive model work - and work quite efficiently. Cells don't re-run just because of edits, but also if the reader interacts with any of the interactive inputs.