Not everything is for everyone. That's life. For example, Hollow Knight is an amazing game. Making it easier would tarnish the experience. That's why the devs made it with one standard mode, then made an even harder mode for big bois. It's the same thing here. Whisper and Zero Hour are challenging missions BECAUSE they have a timer. If you have infinite lives, and infinite time it will never be a challenge because it's guaranteed that you will EVENTUALLY finish it. You're not learning, you're not improving. No time limit and infinite lives would ruin the experience.