Ensure you've followed the steps above closely, as there are some key things to ensure you can install your PS4 update from USB. First, ensure that the USB drive is formatted to the correct formats (FAT32 or exFAT) in step one of this how to. Also ensure that you have correctly named the folders as detailed.
Finally, ensure you have inserted the USB drive while your PS4 is turned off, and that you boot your console using safe mode.