The OP has engendered a host of responses from grans explaining why they cannot 'open their doors' to Ukrainian grand-mothers, mothers and children. I suspect most of these grans are quietly doing what they can, donating financially and physically with household and personal items.
It's naïve to imply that it's just a simple matter of providing a bed or a room. If you host a refugee in your home you will have to share a responsibility for their physical and mental wellbeing and devote quite a lot of your time and energy to looking after them.
How many are in a position to do that - or even have the necessary expertise? You might have a spare room - you also might be out most days, working, caring for others, child-minding, etc. Unless you are fit and well, with nothing on your daily agenda - and have a penchant for caring for people in distress (or even the ability) and are prepared to re-arrange your life, then 'opening your door' is not really an option for most.
That's why we have agencies to help sort out all the numerous problems that refugees face when fleeing war zones, and that's why we donate money, items and volunteer our time, so that these charities / agencies can co-ordinate the response.
Any individual who wants to provide a space and a home, and the caring and nurturing background required for such a gesture will already have done something about it and doesn't need prompting. The rest of us will do what we can, quietly, to help. And the 'hand-wringing' is the recognition of the awfulness of the situation for the Ukrainians and for the wider aspects of the threat to peace in Europe, and the world.
No-one need explain why they can't offer a bed or a room, ultimately these grand-mothers, mothers and children need a home / space of their own, albeit temporary, with all the relevant agencies providing the care for their physical, and most certainly their mental well-being. And as some rely on charity - that's where we can provide the support.
Grans do care, and they are doing what they can, quietly, without announcing it.