When there was more disease about, people did still try to avoid it. They accepted the need for certain limitations on what could be done because of circulating disease. Parents stopped their children from swimming to avoid polio. Diseases like measles and mumps led to children being kept in isolation away from other children, perhaps not being able to go back to school if they might be incubating it.
The idea that a sensible attitude to disease means not ever having to think about it or have our daily life affected in any way by public health measures seems to me to be very much a luxury belief borne of a period in this country when there hasn't been anything new and worrying in general circulation. (Just like antibiotics have let us be more relaxed and less fearful of infections.)
I think people mostly do accept that we're all more vulnerable and likely to die of even common illnesses when we're elderly. If covid had genuinely only killed very elderly people, or killed people by making them drop dead instantly, it would probably be pretty much allowed to get on and do its thing. The problem is that it isn't that neat and tidy. Even if society as a whole said "you know what, if a person over 70 dies of covid, it's no big deal, we won't try to stop it happening", that doesn't really remove the requirement to at least try some basic treatment or keep them comfortable, does it? And if there are lots of them being ill at once, that's a problem. Likewise middle aged and younger people - a much smaller percentage of them might become seriously ill and need care, but if enough people are infected, that can still be a lot of people.
Very frail people not being resuscitated, or no one but a few of the strongest people and pregnant women getting ECMO treatment, is already happening. That's easy. But turning all 70 year olds away from hospitals and saying "sorry, you're too old, you can't have oxygen for a couple of days even though it's all you might need" would be something else altogether. Deciding in the abstract that older people have had a good innings is quite a different thing from implementing a policy that says they get no care at all, and it's something like that that you'd have to implement if you wanted to make high rates of covid manageable. Even without going into the ethics of it (which are grim), it would be very horrible to put into practice.
On top of that, there's the fact that covid seems to be a weird new vascular disease that greatly increases the risk of death after routine surgery, and is dangerous in pregnant women. Dealing with that isn't helped by having a more 'realistic' attitude to elderly people dying, either. The only way to protect people of all ages from those types of covid risks is to have lower levels of it circulating - so then we're back to reacting to it and not having the luxury of ignoring it, even though it's mild in most people.