DVDs were also commonly used as external data storage prior to flash storage becoming the predominant method. Anyone still have their spindle of dvds with a Win XP backup lying around?

Blu-ray doesn’t have that advantage. The only major commercial applications it has been used for is movies and games, and games are already breeching the size that even a 4k blu-ray can hold, and have long since required faster data transfer speeds than blu-ray is capable of(this is why even with physical games, the game has to be installed to the console)