Because you want to be that person who's so in control of your own shit, that no one can point out what a shitload of mess you've already made and need to clean up. Whoever has the gall to point it out to you be damned. Even if you admit your mistake, you still don't want to hear another person agree. At the very least, you want a mumbled statement along the lines of, "well, you did what you thought was best at the time."
You want to be that person who has been doing things perfectly. So much so that you're willing to look all ways except right in front of you. That way, you can avoid seeing what you don't want to see, especially when it's been staring at you right in the face.
So you wait until more crap hits the ceiling or beats you senseless before you realize that, "oh darn! This person cared enough to tell me the truth. Why was I getting mad in the first place?"
Sometimes denial is a fun place to be in.
I've experienced both, really. Gotten mad at the wrong persons for the wrong reasons. I've had other people get mad at me for telling them what I think (after they asked me, of course).
It's easy to get angry when someone tells you the truth. Especially when you know it deep inside, but you're refusing to acknowledge it to yourself.
Me? I'm not the sort of person who constantly asks for other people's help, advice or opinion. When I was younger, I was the sort who'd dole out advice to my friends until I realized that:
(a) people will do whatever they want to do; and
(b) people will only heed advice that already matches what they want to do, so
(c) keep your advice and opinions to yourself unless they really, truly ask for it.
Even if they did ask for it,
(d) tread lightly because of (b).
And yes, be ready - they just might disappear from your life if you tell them something they don't want to hear or know about.
Now, I've decided to be more self-aware of how I react when people are trying to help me. If they cared enough, then I'm not going to make them feel like they're wasting time on a lost cause. Sure, I might lash out at them at some point, but I'll definitely let them know what the heck I was thinking of, instead of giving them a cold shoulder and giving no explanations.
Even if it's easy and convenient to get mad at them, I'd try my best to remind myself of this - they wouldn't help me if they didn't care about me. After all, that's what indifference is for.