Comment by yellowapple

As another data point here: I had to add a TKinter-based loading screen to a PyQt5 app I wrote for work because the app - which takes half a second to start up on Linux - takes nearly a minute on Windows the first time around (and multiple dozens of seconds on subsequent runs) and I know firsthand that my end-users are unlikely to wait that long unless they can see something loading. I suspect it has to do with the sheer number of file accesses for each of the Python libraries and underlying DLLs and such.