More than performance (pure Python can be too slow, but NumPy is usually fast enough), this is what I miss when using Python.

There's currently no good solution for bundling Python code and the interpreter into a single binary. PyInstaller works, but the resulting binaries write lots of files to `/tmp` every time they run, which is a hack that leads to long startup times. PyOxidizer avoids this, but includes the entire standard library in every binary, making them too large by an order of magnitude.