Python's interactive interpreter makes it pretty useful as a shell, for iterative development, and crucially useful in a Jupyter notebook. I've also found CircuitPython's interpreter to be bonkers useful in prototyping embedded projects. (This, on top of the nice datascience, ML, and NN libraries).
Swift just wasn't doing the same things. And even if it did, Swift would compete with other languages that were understood as "a better Python", like Julia. Even then, Swift only came to Linux in 2016, Windows in 2020, and FreeBSD less than a year ago with WWDC 2025.
I think it doesn't help that the mid 2010s saw a burst of Cool and New languages announced or go mainstream. Go, Julia, Rust, TypeScript, Solidity, etc. along with Swift. I think most of us only have space to pick up one or two of these cool-and-new languages every few years.
Swift has had an interactive interpreter from v1. Even scripting in Swift was supported from the start.
What it really needed back then was ergonomic APIs for this kind of programming.
Why would anyone in 2014 adopt Swift as a quick prototyping/scripting language when you can just do os.path.join() in Python (Swift's path APIs have always defaulted to the NextStep–era stuff), or subprocess.run() (Swift still defaults to NSProcess).
Today, the picture is different; swift-subprocess and swift-system have improved things greatly.
Swift just wasn't doing the same things. And even if it did, Swift would compete with other languages that were understood as "a better Python", like Julia. Even then, Swift only came to Linux in 2016, Windows in 2020, and FreeBSD less than a year ago with WWDC 2025.
I think it doesn't help that the mid 2010s saw a burst of Cool and New languages announced or go mainstream. Go, Julia, Rust, TypeScript, Solidity, etc. along with Swift. I think most of us only have space to pick up one or two of these cool-and-new languages every few years.