I am coming very late to this thread but there was some discussion of how the Enigma system of using a reflector introduced a weakness. The advantage was cost as you do not have to have a mechanism with a switch between encode and decode. Similarly the pawl and ratchet mechanism limited the number of notches that you could have without reducing the number of characters before the Enigma came back to its initial state which also weakened it (the Abwehr Enigma movement was better but more expensive). Thus the driving force was cost and perhaps reliability. Germany built far more military Enigmas than the USA built Sigabas/ECM II and far more than the British built Typex machines.
Since this thread is about books, perhaps I should recommend Rebecca Ratcliff's "Delusions of intelligence : Enigma, Ultra and the end of secure ciphers" to look at why the Germans did not understand the danger of their approach. One might also look at "Fall Wicher", the German investigation into the evidence that the Poles had broken Enigma
Case 'Wicher' – Information from the war diary of Inspectorate 7/VI.