I will say that the total number of onsite guests who might take advantage of an OBB ticket presale might be fairly small? I don’t know the numbers, but several here have posted about how many people can do resort guest EE and that the number overall is small. And folks would have to know that they were going and book the hotel several months in advance to take advantage of any pre-sale.
In any case, DLR does offer PPH, DLH and GCH, at very different price points (we have both the GCH and PPH hotel booked for an October trip and the PPH is less than half the price of the GCH, so I do feel that ”onsite” is not so exclusive as to exclude everyone except those that have very high budgets; that said, they don’t have a “value” level like the WDW resorts). As an onsite guest, the perks are getting less and less and the price just keeps increasing. So priority access to something like OBB tickets might be an idea for the future for Disney, but only if hotel bookings start to soften (at least for our October trip, no indication this is happening as all Onsite hotels are expensive, yet also sold out!).