Its not all about cost and long lasting bullshit, Honda's Manual transmission does not accept any other oil other then Honda genuine gear oil. I have tried it, since i was unaware about the exact lub requirement for the gear so went for ZIC 75W-90, transmission became hard, could clearly hear grinding noise, gears used to stuck, finally drained and shifted back to honda geniune gear oil and it became smooth again.
thing is, if Honda would have mentioned the oil details(Data) on packing then things would had been easy in picking an after market product. So not mentioning on Honda packing is like a marketing tactics for Honda so consumer sticks with their product only.