That is just your opinion and how you want the game/event to work unfortunately. It isn't how the devs designed it and and they did state the decreasing odds up front, but again there definitely needs to be better in-game communication of this.
Not to make you angry, everyone has the right to their own opinion. If anyone should be angry, it should be me since I have yet to score the 10th item in all 3 events. LOL I've seen some who have them all, some who said they never spent gold, some who got them by the 3rd day not even using gold. (or at least they claimed) So it appears it is possible to get them but I have the same luck as I do in winning the lottery. You know I had 8 with like 5 days to go in the event and still made it only 9 the last day and I opened 2-3 times the number of boxes of some who did get it. Random.
I wish you the best of luck next time though buddy!!!