ANSWER: One thing about the British, they liked simplicity. Most of the engine designs all used the same Lucas distributor. If you talk to most British car enthusiasts you will hear what they think about the Lucas distributors, but the positive was that it kept tooling expenses to a minimum. Suggestion: It is in your best interest, where you can, do upgrade to an electronic trigger distributor.
ANSWER: The short answer is because it isn't. The more accurate answer is that the various drive dogs are specific to each engine, matched if you will. Since wear is very limited it is perfectly acceptable to use the original drive dog.
