> around 2015-17 - Swift could have easily dethroned Python.
Why could it?
> it was simple enough - very fast - could plug into the C/C++ ecosystem. Hence all the numeric stuff people were doing in Python powered by C++ libraries could've been done with Swift.
Half a dozen languages fit this description.
> the server ecosystem was starting to come to life, even supported by IBM.
No, not at all. Kitura, Vapor (a fitting name) were just a toys that no serious player ever touched.
After that, and IBM losing interest, Apple did hire a few competent people (including contributors to Netty and Akka) to build the Swift Server Workgroup.
But I don't know why I'd pick Swift on the server when Rust is better in almost every dimension, with a thriving and more community-driven ecosystem.
I think it's not about that but about dogfooding Swift on the server. Apple uses Go, Java etc for a lot of its server components and refused to invest in hiring people that would extend the ecosystem for server Swift.
Thats the problem.
It certainly doesn't help, but among big tech, Apple is not the only company where teams are siloed and independent. Microsoft has people writing Java or Go instead of C# too.
I assume the server side usage is not zero, but not enough to reach a critical mass, you're probably right there.