There's a difference between reinventing ten wheels ten different ways for ten apps, and reinventing one really big wheel. It has to be self-contained enough that other apps can use it without having to roll their own anything, so all of them has the same API.
One of the problems with "just use a different P2P VM" is that it probably wouldn't solve the problem of having a server your mother could use. You'd probably still have to install and setup Apache and MySQL and ElasticSearch and whatever, even if someone implements the perfect transport protocol and platform. For Urbit you just run it, which can be hidden behind a pretty "click to start" button that pings our to AWS. Hence, one big wheel.
If you do see an Urbit-like project that has the same goals, I would be ecstatic to hear about it though. I've basically had "urbit but different" on my TODO list since I first saw about it.
You get the irony of complaining about how every competing design has had to "reinvent several wheels", right? The system you're advocating reinvented ASCII.