It added an extra element of strategy to it all which I enjoyed. I really hope they keep adding something like that. Tbh, they should've just made it permanent and just keep adding more prizes along the way. Why did they remove it in the first place?
People worked out the prizes though. I think the game was more interesting, but also too fast as some of the prizes were way more busted than others and they never bothered to balance them. Plus they need to find a way to slow people down from getting busted tier 6 minions, not make it easier.
Asking why they removed it is looking at wrong, they were never meant to be a permanent addition. They always had a finite period of time they were going to be in the game for.
I personally liked them, I don't play BG all that much though so I may not have gotten tired of them. They seem to have been pretty popular and I imagine they will continue to introduce mechanics for a limited period of time, to keep the game fresh.
I'd rather have 3 different sorts of these prizes and similar mechanics that aren't in the game all year than have the same mechanic as a permanent fixture.