"The Golden Age of Handbuilt Bicycles" is much catchier than the more accurate "The Golden Age of French Bicycles"
Be that as it may, it is a wonderful book, one I keep going back to ... again and again.
As for why Brit framebuilders didn't make their own parts: I've got two conflicting theories:
(1) they didn't have to, since they had many good bikcycle parts makers supplying a huge variety of parts ... and were not averse to using imports.
(2) they couldn't charge what the top French builders were able to charge
Amir Avitzur
Ramat-Gan, Israel