what I don't get in bald terms is why people out there can't understand that a small percentage of a huge number - will be a large number
I don't think many at all fail to understand that, it's a mischaracterisation of the opposition to restrictions, it's the sort of straw man rhetoric common online. The disagreement is that the harm caused by restrictions is worth the benefit of spreading out that "big number" over a longer period. Even overshoot is significantly less relevant when omicron requires over 90% infection/new vaccine before any sort of herd immunity arrives.
It may seem callous, but the people do understand the big number, they do understand it will cause deaths - but they also understand that the NHS budget cuts cause deaths, that car policy causes deaths, that smoking and lack of exercise cause deaths, lots of things cause deaths, the balance is that society deems them acceptable, covid is not special.