Sure, that's another category and different considerations. I've worked at an academic lab with a limited budget where we set up file servers, but couldn't afford to do anything approximating 3-2-1. We did a nightly backup of a tiny part (most important) of the data onto another server in a different building, but like 90% of the data was just YOLO (well, RAID, but that's not a backup), and that's just how it is. Disks are pretty good though, they don't die often nowadays, and when people accidentally deleted their data, it was just gone. Would have been cool to have a backup of everything, but even just pulling out a nightly backup from a dense server with dozens of terabytes isn't simple and you don't want to slow down the server by constantly reading just for constructing the backups. It's a tradeoff.

Redundancy has costs and those costs can be spent elsewhere like having higher quality or bigger disks, or a faster network switch or better CPUs etc.

In theory, it would also be better to own two cars instead of one, because what if the first one gets in an accident or just breaks down. Yet, not everyone can afford that. Should you just buy two half-as-expensive cars than what you can buy one of, so you can say you have a "backup"? Likely the two half-price ones would be so much crappier that the one good car would cause you less trouble in expectation than driving a shitty one and then having another shitty spare one, both of which will constantly have issues.