As an outside observer of this beef tallow trend, it looks to me a lot like a fad driven by some internalized machismo: "It's not proper food if it's not from a dead animal." While this is not unique to the US, apparently believers of this in the US reached a critical mass enough to make it public policy. I don't doubt that one can find health benefits in beef tallow. But I also vividly remember ads in the 80s and 90…
Aren't Americans the kind of people who will cut the fat and gristle out of their rib-eye and leave it on the plate? And it was like a thing of pride to not eat the fatty part because look how rich we are ... Now they suddenly all into slurping beef tallow. What?
What has changed is we have learned that fat isn't as bad as it was made out to be - it doesn't seem to have as large an effect on health as thought 40 years ago. That doesn't mean it is healthy - though some take it that way.
It was once observed that vegetarians being healthier than others could be explained almost entirely by vegetarians being less likely to smoke - something studies generally didn't even try to control for and so we don't know if that observation is true. There could be some other unknown factor in play as well that because it is unknown we can't control for it.