Because it makes us challenge our ideas and offers us an opportunity to improve our work. It’s not always about seeking reinforcement that you are on the right track. You want to be challenged. How else are you going to be able to persuade the other party that your idea is going to work?
Don’t take criticism as a negative, but rather as a positive step towards your goals. Even if you don’t take a single piece of advice on board, at least it made you challenge your ideas and that is a good thing!