1) that's the way it really is
2) it makes you have to make a strategic decision with a little bit on uncertainty, and you have a classic risk/reward problem to solve in many cases. I could sell this player now, and hire a non injured substitute, but I'm going to probably pay a premium for that... or I can hope that this guy gets better before the playoffs start, or this important game etc. Giving slightly imperfect information makes this an interesting choice, without the uncertainty it wouldn't be interesting.