For you discussers I have the following reasons why the East Asian and the English (at least with Churchill) got protective:
"Archery and Gunpowder units receive Drill I and City Garrison I automatically
Double production speed of Walls and Castle"
First protective does mean obviously the defense of their cities. No doubt the Asian peoples are remarkeable in those terms as well as Churchhill is. Second this trait is not purely defensive. Above all it strengthens archers, rifles, infantrists as well. Meaning: The longbow, cho-ko-nu, the red-coat etc. pp., they all have drill I with their leaders, with a barracks drill II and soon drill III, maybe IV against some barbs.
Which means that protective also makes strong attacking (and defending) archery and gunpowder units. And who does not know the power of the English Longbow or skill of the Chinese bowmen (movies

)? Whereas you cannot say for other civs/cultures that they are world-wide know for there superior archery, rather for their imperialistic behaviour or their sophisticated bureaucracy or their traders...
I think it is just that easy and has few to do with "hey they're all protective" because they're all the same great isolationists. Though that MIGHT be one aspect among others playing into this.