I would imagine other countries manage it because it's been an inbuilt part if the system for a long time. And it's evolved as times have changed. Or the countries in question have a cohesive sense of "national pride".
In the UK we have other means of achieving what NS will allegedly deliver if youngsters are interested. Scouts, Guides, Cadet forces, DofE etc. Most secondary schools do charity stuff.
Mandatory "volunteering" is not the way to go and given the areas of civic service mentioned, if this is for 18+ it directly interferes with university and other FE, plus smacks of free labour and may well push out volunteers in other demographic, or jobs. Or apprenticeships. It's logistically a nightmare to implement, unless the trajectory of every teenagers life is going to be re-structured from 6th form onwards - which I suppose might be in the works if they're aiming to start it in 2025.
But it hinges on re-election, so it's likely (hopefully) an absolute pipe dream anyway, or a fever dream, or the result of one line too many in the Downing Street loo.
Whichever way you look at it, it's nuts.