For 1: most people do not care about diseases that do not matter. Most people consider the common cold normal and acceptable. I was very sad such research never went very far, for I believe viruses are way more deadly that we think: as we know now that the EBV can cause many bad things long term, there is no reason to think other viruses can do the same. The fact that these 2 separate diseases are called the "kissing disease" (EBV) and the "common cold" (coronaviruses) gives a fake sense of safety. SARS was the perfect scare to get research started!
HOWEVER, most people do not care about viruses, and problems in general besides imminent danger. If you too care, realize we are in the minority. Before covid19, most people though the wearing of masks when one has a cold in asia was overkill. Even now, in the midst of a pandemic, the wearing of masks is a hard sell. I fully expect all basic precaution like transparent plastic sheets in front of the checkout to be gone as soon as the pandemic is over, because we are in the minority.
For most people, the experience of directly seeing the person doing their checkout is preferable to the alternatives. It makes them happier. It is not hard to expand that to other issues: even for a virus like Ebola, research doesn't get much money. Clearly, it means that at the population level, we just don't care.
2. Have you noticed how people play various games like Zynga, which accomplishes nothing? Just like videogames in general: unless you are being paid for playing (professional player), you are getting nothing out of it, except maybe better reflexes - but you could achieve the same result in much less time. Social networks are the same. What am I accomplishing here? Nothing. You could even say, as I often talk to people who reject my premises, HN makes me unhappy. Yet I post here?
So you must consider that what we consider make people, you or me unhappy is an oversimplification. We must gain something else out of this - maybe a dopamine hit?
Social networks are all in competition with eachother. You will prefer the one that gives you the best overall experience, the largest dopamine hit with the lowest unhappiness.
This social network increase overall happiness. There may be more than one: facebook for regular people, HN for hackers, Twitch for gamers, etc.
It's hard to overcome the fallacy of composition (the tendancy to extrapolate from our own experience to the population level): what makes us happy make make 50% of the people miserable, and vice-versa.