Your questions prove you don't have the "SMART" to understand so let me make it a little clear!

Why people from different nationalities?

Respect for the dead can come from any nationality!

Why so few British?

...and you obviously know there who was British and who wasn't! Many were at work at the time and came earlier or later and was not there for the photoshoot!

Clearly as you said "SMART ppl would get it already"!