I'm not sure that the general public is aware of this. I believe the perception is that older couples think they have to stay in their home, and that is no the case. You can downsize and keep the increased nil rate band.
One concern when the government first discussed the new allowance back in 2015 was that it would discourage older couples from downsizing or selling in order to move into residential care or the home of a son/daughter etc. But the rules have been tweaked so that the allowance is still available to those who downsize or cease to own a home before they die, provided the deceased left a downsized residence or assets of equivalent value to direct descendants. Downsizing or the sale of the property has to have taken place after 7 July 2015, but there’s no time limit on the period between the sale and dying.