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.