The reason why the 0-49 bracket is most low is because most people don't start suffering from more than one of these typically if they're healthy.
However, of those who have caught it, they are at much higher risk to die from it than not. Not everyone has that genetic lottery to be on the safe side. where they don't have to worry about it. You can be 10 years old and suffer from a lot of these things. When I was a kid, I had cardiovascular disease, had asthma and I was on the Soccer Team and Baseball team. I've always been in shape, but I just have a bad lottery on genetic disorders. Lots of other people do. What we also have to consider as a possibility, is that there are those who didn't take this virus seriously, or practiced poor safety techniques.
The rest of us, we've been stuck in a house since March because we know that we're at higher risk. I now take a medicine which suppresses my immune system. So, let's play COVID BINGO - Asthma, Cardio Vascular Disease, Used to smoke, Suffered pneumonia last year, whenever I get the cold I end up getting bronchitis, immuno suppressed.
Oh and this is hilarious, as if shit couldn't get weirder. Even though I don't have Hepatitis, basic blood tests will always flag me as positive, but a more thorough blood test will show negative. I'm expecting my second child with my wife and she tests negative. So like, wtf? lol.
At the end of the day, you don't need to even combine all of those. Those with asthma/respiratory problems are likely to be at the highest risk. Followed by cardiovascular. The other part about this herd immunity, not everybody (even if they aren't at risk) wants to risk dying from this virus. Even if it's low, it's still higher than the flu. Those that survive still suffer chronic issues as a result of COVID. Who wants to chance that? That's like saying "Let's play Russian Roulette with a 20-shot revolver." (I know, no such thing really exists... or do those pirate ones count?)