Blue-Ray Discs are basically the only viable WORM (Write-Once-Read-Many) that is available to normal and small scale professional users. The cheapest alternative, Tandberg RDX is a few hundred bucks per TB. And these are far inferior in terms of protection against outside influences compared to BD media.

And considering that a lot of professional data (e.g. tax reports) are legally required to be saved on WORM in a lot of countries it is indeed an issue, even more so in times of crypto/ransomviruses. None wants to loose their precious baby or wedding photos to a untimely virus. And no, normal Dropbox/OneDrive is no proper backup. And USB drives/external harddrives degrade over time, especially if not used.