Because this particular task really feels like the killer app that we should already have -- frictionless, non-heirarchical notes that you can just dump into the system and then retrieve based on a few relatively simple axes, date, keywords, a little semantic analysis, etc.

Where I think people are going off the rails is thinking that this can work as a business. I'm hugely skeptical that there's a market here; businesses rely on some measure of "if you don't pay you can't have this part of the thing." -- and even if a startup is able to make this work, it's likely that the "value-add" will be easily replicable into something free (as in freedom) owing to the nature of this being a "power-user" thing.

For example, none of these things promise too much more than, e.g. Zim-wiki (longtime user here) -- which itself is extensible either as FOSS, or simply owing to the fact that it saves in Markdown-ish, immediately MAKING it extensible anyway.