To be able to use some that were advertised on day 1 but haven't been added until now.
I wouldn't complain about an intelligent flight mode or some minor stuff that would give extra functionality that was not part nor an advertised feature at launch e.g. the modes from the Spark being backported, but in the case of the
goggles they were announced at the same time as the Mavic, DJI made a huge deal about the combination of both products, and it has played a significant role in the decision of many of us early customers of the Mavic to go on with the purchase.
Nowhere does it say that to use them properly you have to cripple your Mavic as a result of the required firmware version including unrelated changes. If DJI didn't take 8+ months to release the
goggles they would probably work properly in .400, but since they took ages to be able to provide them implementation of the
goggles' features in the Mavic fimware that ended up being delayed to later versions.
Not even talking of anyone who will receive their Mavic with .800 or later even though none of the marketing materials will have been updated. Nor the fact that while possible staying on current versions needs specific knowledge and care that is not to be reasonably expected from most users.