Unfortunately, serious mental health issues are common in my family. My son has schizophrenia and a serious anxiety disorder, my husband has a similar set of diagnoses (son lives in supported accommodation; husband is in residential care) and my youngest son has a serious anxiety disorder and an eating disorder. I was also hospitalised for an eating disorder throughout my mid teens and twenties, and my mother was hospitalised twice for hypermania.
In all our cases, one of the consequences of serious and chronic mental illness is loneliness and isolation. Mental illness often leads to self-isolation, but it also can manifest in behaviours that are difficult for others to cope with. Certainly my eldest son's behaviours and my husband's behaviours when they had psychotic episodes were impossible to deal with, and my behaviours when in the grips of an eating disorder were impossible for my family to manage.
So, yes, I agree, contact does tend to fall away . It would be nice to think that professional services would pick up the threads of support when friends and family can no longer provide adequate help. However, in my family's case, I have found this not to be the case. For example, my eldest son is visited every week day by one of his care team, but throughout the rest of the day, he is alone. He frequents places where he finds people who will be kind to him, a local shop where the owner will let him sit and talk to him, a cat cafe where 'gentle' people congregate. The interactions are short lived, but they mean so much to my son. My husband likes to talk, but there are very few people in his care facility that have the time or, unfortunately, the ability to have a conversation with him.
Thank you OP for raising this subject. With the current focus of the media being firmly placed on the 'cost' of mental health difficulties to the economy, it is helpful to consider the realities of living with mental illness.