Part of it might be applying the many patches of definitions and stuff, but it’s probably mostly just loading a shitload of png files in memory.

Even worse, even after years of updates, the several literal minutes of loading on a HDD happen on a completely unresponsive, static screen (Windows even prompts you with that “kill the app or wait for it to respond” pop-up if you alt-tab out of it).

There’s a mod to add a progress bar to that initial mod loading. Yeaaah.