The primary reason more older adults in western countries live on their own today than ever before is

The simple answer is a Better Health and Stable financial position

In Developing economies where a general household is low-income, older parents are seen as the responsibility of the children.

With poor medical facilities and a non-existent government pension program, most people aged 60 + cannot work, have low income and suffer from diseases.

In such a case, their children take care of them and live together in a house.

In the Western world, adults earn better have have better medical facilities, which leads to more Independence, freedom and non-reliance on the family.