Pick 5 and 8 for a hbf seems a bit excessive, even though McGrath is supposed to be very good, it still seems a bit much to me.
The real reason is to avoid buying their academy players with high picks. They are so advantaged over other clubs it's actually insane.
If they keep pick 6 then they will have to use it on an Academy player. If they get rid of it for Pick 1 then they a) get to pick whoever they want and then b) get that same academy player with junk picks.
So basically they are laughing all the way. I hate them so much. No, actually I hate the AFL for creating such a lopsided situation in the era of equalization.