How odd! But I believe you are right [1], all two dozen Apple keyboards have the option (aka "alt") key, including the "British" one, but not the "English" one... (Who's the imperialist now ;-)) Perhaps the idea is that the average user only needs the option key for non-ascii characters like £, so Americans won't need it.

[1] https://support.apple.com/en-us/HT201794