They read stuff off disk 1-4 bytes at a time and malloc() in a loop, then deserialize which calls its own malloc(). Its tiny malloc()s all the way down, and strlens for sure https://nee.lv/2021/02/28/How-I-cut-GTA-Online-loading-times...

The result is usually one CPU core running at 40% with sporadic disk access while you stare at Loading progress bar.