I think OP meant to compare a known hard task vs an unknown hard task. Both are hard, but first is known to be possible to finish, but the other not so.
A widely accepted method fur judging at least subjective risk when there are insufficient facts for truly objective measure is to ask how much you would bet on various outcomes - such as whether P=NP is solved before New York's 2nd. Ave. subway is completed.
So, in a sense I think that part captures the problem. People object to testing backups using the logic of "with our shitty processes, it will be dangerous". I suppose you have companies with a logic akin to "due to being cheap arrogant, we have shitty processes" -> "due to shitty processes, our processes are fragile" -> "due to being fragile, we avoid anything that would stress our system" -> "due our system not being able to take stress, we just pay ransomware instead of stressing system with a backup".
It seems like we've reached to "throw-away enterprise" level. Build it cheap until it breaks, then walk away when the fix cost is too high. There's a cost-benefit to this. Reminds me of bandcamp and other declining sites that just vanished one day with information some would consider valuable.
It's difficult to do, yes. But it's difficult in a "dig a tunnel through that mountain" way, not in a "solve this mysterious math problem" way. It certainly could be done. It would just take time and money (money including hiring people).
People constantly point to the difficulty of backups and the difficulty of hardware level separations between systems. But these are merely difficult and costly. "No being hacked" and "writing always secure code" are impossible and so they won't protect from backup failure.
And yes, companies would rather spend money on other things. That's what it come down to.