Grandparents only work if your parents retired or your grandparents are alive and functional. Current generations millennials and Z have grandparents dead(shorter average lifespan, waiting with having children) and working parents(economic situation, better healthcare). Not only that, but you also need to live close by. We are migrating way more than before, there are whole cities in Europe and US left with retirees. You also need to have a larger house to host grandparents. Millennials have a worse economic situation than boomers.

Current life of young people look like:

  — Get expensive degree
  — Move to expensive city for jobs
  — Hard to find partner
  — Cannot afford to start family, postpone children
  — Have children without family support 
  — Get into high level of debt

There two things happening

  — People have less or no children. This lead to increased taxation and increasing retirement age in many countries. It often causes social unrest when governments try uncontrolled external immigration to fill the gaps. 
  — People try to live frugal lives, reduce spending and try to save for retirement individually. This disturbs housing market and stall country economy and destroy luxury brands.