I don't believe the "syntax win" scenario. Python is also ugly, due to the required indentation, like yaml.
I believe more in the ecosystem, specifically how the computer vision and machine learning movements have adopted python extensively as frontend language (the heavy weightlifting is still doing in C++). The exploit of numpy has brought many many use cases into the language as well.
That 'ugly' required indentation and whitespace also made Python easier to read, especially for newbies and casual coders. A standard visual structure and a syntax that is pretty close to executable pseudo-code lowered the barrier to entry for a lot of people and made Python feel 'approachable'. This perception that it was easy to use helped increase the network effects other have noted.
PipeNet was conceived in 1996 (https://cryptome.org/jya/pipenet.htm), before the USNRL work was made public in 1997 (IIRC), so definitely independent, in as much as these things are ever truly independent. Both are derivative of Chaum Mixes (1979), which had become popularized as anonymous e-mail remailers in the 1990s.
P.S. Not a comment about project name clashing, just thought it would be interesting to point out. Wei Dai's PipeNet is all but forgotten these days. But I had came across it (on sci.crypt?) before stumbling on the Onion Routing web page.
Definitely a blast from the past. One of the things that made PipeNet very interesting compared to its contemporary peers (e.g. onion routing) was that it used fixed size pipes with constant traffic. An observer would be unable to know when traffic was being sent down the pipe so correlation attacks become significantly more difficult. Pair it with some probabilistic encryption like Blum-Blum-Shub and you can party like a late 90s cypherpunk.