You probably did this, but just double checking. You have unzip EA5T-14D544-BA.ZIP and then place the unzipped files on a flash drive to install the update. I used a PC with Windows 10.
Also, since you are using a Mac it has me thinking because my wife uses a Mac and the format on her storage devices is different than the storage devices or flash drives that I use on the PC. More specifically, if you want to move files to and from a storage device on a Mac, the device has to be formatted in "Mac OS Extended (Journaled)" vs a flash drive on a PC that has to be formatted in either "exFAT or FAT32". So, if your storage device had the Mac OS Extended (Journaled) format, that may be the problem. You may need to reformat the storage device to exFAT or FAT32 before placing the files on it. Purely a guess, but may be worth a try.