The sad thing is that it is exactly these people that can benefit most from a voice assistant. I think what’s needed is either a separate model made by someone else than a huge corporation or, realistically because of the overhead involved, a mode on the ones you can already buy that caretakers can turn on that doesn’t allow you to purchase things and has apps specifically for elderly people.
Of course Amazon wouldn’t be earning money on those but the good PR alone might make them do it anyway with a bit of public pressure.