Maybe Brisbane were going to move onto other options? No-one really knows what has been offered for that pick.
Melbourne have 1703 points between 28 and 65 - they may have made an offer
Saints have 1019 points between 27 and 47 and could have offered future picks to bulk the deal up
Giants have 910 points between 37 and 56 and also could have offered future picks
We might also need that Pick 20 to unlock other deals, again we have no idea whats being discussed behind closed doors so might have been pushed into getting the deal done asap rather than wait, as surely Brisbane wouldn't have wanted to wait either as it takes out the chances of other deals occurring.
I would hazard a guess that the same people crying blue murder over the pick trade, would have also cried blue murder had Melbourne traded those picks above for Brisbanes pick as "Blair being asleep at the wheel, what are we supposed to do with all those later picks now".
Whilst yes we may appear to have gone a bit early, but what else? What if they'd traded it to someone else, and we couldn't trade those picks out, we don't have enough list spots for those and the expected picks we will get, so again people would cry blue murder over "losing those picks as we didn't trade early enough".
Maybe wait and see what happens across the full trade period rather than fixating on 1 trade.