I think we are all aware that it's a time management game. But what's also factored into this particular game is the RNG that determines what you get. In the other games, you know that you're cooking recipe X, you will have it ready in X amount of time. If you crossbreed pet A with pet B, you will get pet C after X amount of time. With the eggs/breeding in DS, you have no earthly idea. And if you see the fail coming, you have no choice but to wait for it to be ready only to be potentially disposed of immediately.
I think the non-expiring aspect is the only saving grace for it, because had it been where things still expired, this game would be highly disliked all across the board, I'd imagine. This way, it somewhat lessens the blow of having to be left at the mercy of "luck". They all can't work the same and I suppose it can be a good thing that it's different, for some. In the end, the game is whatever it's going to be, so you just have to take it or leave it. :/