Many people are alone with no one in the world.
Myparents are dead and I have no brothers or sisters. Cousins in Australia and New Zealand who I have very little contact with. A much older cousin in London who I can go months without contact with although we get on very well.
If it wasn't for DH, I'd have no one who would notice if I disappeared- especially if I had moved abroad and lived somewhere in a small village.
It's very easy to end up anonymous in our society. Most of us pay lip service to really caring about elderly people who are alone or colleagues who have no partner or family. I work with someone who is divorced, in her mid-60s and without children or siblings. She spends every Christmas and most weekends alone, never has a holiday. I occasionally meet her for a coffee on a Saturday or go to the cinema with her. She's very nice but has said to me she feels invisible to others and that most people never ask about her life outside of work. We are having DH's parents and grandma to ours for tea on Boxing Day and I invited her but she said 'No thank you' very politely. It's not that she is doing anything else but she has spent Christmas alone for 25 + years and feels she would be awkward and uncomfortable and it's just easier now to be alone. I'll ask her again nearer the time but I don't think she'll say yes. She retires next year and has no plans at all.
I have a 92 year old aunt (my dad's older brother's wife, not blood relative) who I have done quite a lot for since her husband died but she has fallen out with me because I won't jump to every phone call and demand for this , that or the other. She expects me to do everything she wants done and a) I don't have the time, I work full-time and have 3 small DC and b) I don't want to. I am not inclined to go round at 9.30pm because she can't set her clock or wants her laundry collected and done or has fallen out with her carers and wants me to sort it out at that time of night. She has no relations, apart from my cousin in London who rings her once a year. She will die alone. A carer will probably find her if she doesn't die in hospital. She has a sister who she has no contact with because she said so many nasty things to her, her sister cut all contact.
I could do more to help both of these people but I am choosing not to. Both of them are really lonely. My work colleague is nice but can't see a life outside of being alone and (if I'm honest) I don't want to get into a 'routine' with her where she expects my time. My aunt has upset people all her life and caused upset in my family for decades and I have no desire to be any more involved with her. I am quite relieved to have fallen out of favour with her.
I think it is even harder for men who are alone as they age, or for people who come here from another country and are alone, or for anyone who is vulnerable in some way- perhaps an addict or an alcoholic or suffers from depression or other mental health issue. People don't tend to open their families to others.