I actually don't just mean 7, which is really extreme! Some posters do 830, etc. In the UK generally it's true that kids go to bed early.
Also, if you've lived in different countries, you genuinely see the difference in chaos and stress – especially in households with multiple kids, instead of just 1 quiet obedient kid.
Of course every household differs. But, if I were to make a generalisation –
In the country I lived in, come dinner and post-dinner time, you see and hear kids still chattering away, playing with their peers, or chattering and socialising happily with adults.
Then, a common sight in public was seeing kids merrily, relaxedly returning home with their family (and I think a lot of British families don't have the time to have dinner out). This would be at a shocking hour to many British parents.
All my friends' kids would then naturally / automatically start going to bed, wanting to rest after a long fulfilling day of genuine family bonding and playtime. Of course I assume there are still those kids who throw tantrums or are difficult sleepers. But can you not see that in general it's easier to wind down and naturally ease into bedtime over hours?
And the parents themselves are more relaxed of course which makes a big difference in family bonding. Not 'I have to rush home from work, dinner, 1 hr 15 mins of family bonding, shower, bedtime' day after day after day