The fact is that people who remained isolated got it. The majority of those however, are poor or elderly, live in apartment buildings or other shared housing complexes where air supplies are shared. Hence the Lancet indicating the virus can be found in air ducts where the only pathway is through the air.
I'm poor. I've been poor most of my life. I have lived in those types of communities all my life. I have to say that elderly people are likely to come into contact with people even if they do isolate because they are more likely to need assistance. They might have their food delivered or have someone who 'helps out' and they have to go to the doctor more frequently than the average person. This means traveling, and going into buildings, and other average activities that would bring them into contact with other people. I've been working as a customer care rep for a state unemployment agency during the pandemic and I guarantee to you that those people who 'isolated' did not consider the people delivering their food, or the family members who stopped by to help them but didn't live with them to be outside of their 'isolation'. At least two thirds of them would have assumed that those people were included as part of their isolation. I've had those conversations with elderly people and they assume that anyone asking feels the same way they do and defines isolation the same way that they do... meaning isolating from everyone who isn't necessary in their lives... not isolating from anyone who could bring them into contact with the virus.
As to poor people.... they are less likely to have groceries and other items delivered because they can't afford that. That means going to the store or the food bank when they need things and that means coming into contact with people who could spread the virus.
I've lived in the types of low economy housing you mention, and those places rarely have good air systems. I have no idea if COVID can or cannot get into air ducts, but I do know that low income housing often has air ducts that don't work properly.... either putting out too much air or not enough.
So... even people isolating could come into contact with the virus in very normal ways. We don't know the specifics of anyone's situation. Offering up anecdotes means nothing. But even giving specifics as has been offered... doesn't go into the detail and fully explain any situations. The reality is... we don't know. We don't know how much the virus spreads when people are in isolation because very few people actually have the ability to fully isolate themselves. We also don't know what the realities of the spread are because the virus hasn't behaved in the ways we are accustomed to.
I spent the first year of the pandemic with little change in my life. I had an essential job that did not bring me into any more contact with people than it had before. I worked at a medical lab, but it was a clean lab that didn't test anything that could infect anyone. Like I said before, I'm poor. So I continued to go to the grocery store, I continued to ride the bus, and I continued to work. I had been wearing a mask for 10 years prior to the pandemic so that wasn't anything new either. And I didn't get the virus during that entire time. Then for the next year I moved and lived with family. I self-quarantined (more so because my brother had cancer and I didn't want to infect him with anything), I have all my food delivered. I do all my shopping online. I only meet up with family when we can do so with social distancing. And I still haven't had the virus. The strange part is that I'm a high-risk individual and I have always gotten whatever sick was going around. But I haven't gotten COVID. I got the Johnson&Johnson vaccine because I'm a high risk individual. I would rather be safe than sorry. I didn't have any blood clotting problems. I didn't feel any negative effects from the vaccine at all. And I still haven't gotten COVID. My brother-in-law who has always been low risk and rarely gets sick, got COVID and died within a week. I personally, think that we just don't know enough to even know what we don't know with this virus.
But I should say... to me COVID isn't much different than the flu. Both could kill me. In fact there are so many things that can kill me that it is just one more to add to a very long list. People who are familiar with dealing with contagious infections that can kill them aren't freaking out over COVID. I already washed my hands or wore gloves when I needed to. I already wore a mask to protect my lungs, even when it was hot and uncomfortable. Most of the more substantial precautions I have taken have been to relieve the minds of my family who I actually want to see and spend time with. Not everyone is hyperventilating about COVID. And I will be getting a flu shot when flu season comes around. I doubt I will get the flu this season as I'm not around people as much as I used to be. I'm not riding on the bus anymore with poor people who don't know how to cover their mouths when they cough and sneeze. I'm no longer working with children, as I did before the (my part-time job was lost when the daycare shut down because of the pandemic), and children definitely spread the flu. I don't know if this year will solve the riddle in this thread because more children have gone back to school and we aren't in flu season yet. We might hear just as much about the flu when that time of year comes around. Especially if people aren't getting flu shots... I can imagine people will think the Covid vaccine works on the flu as well, even thought that isn't true.