Why is OBD2 not a subdissector of 15765

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Why is OBD2 not a subdissector of 15765?

The standard seems to say it rides on top of 15765 in the case of CAN. I do recognize that it also says it can ride on some other Physical layers but Wireshark doesn't support those. Officially riding on top of the 15765 dissector would also solve my second gripe that the current OBD2 dissector requires 8 bytes in the frame to dissect, which I can't find spec support for. If this or that ECU requires 8 bytes, that's a whole other issue compared to what's allowable in the spec.

But I'm also fairly junior in the industry so, correct me where I'm wrong.