Because it is way more secure than iOS. Yes, you read that correctly. Look at the results of the most recent Pwn2Own event before you even think about replying to this.
Any platform can be compromised if you install malicious software on it, even the almighty Linux. This shouldn't take anything more than a grade-school education to understand. Just because you aren't smart enough to figure out that random pirated apps may be malicious doesn't mean that the rest of us should live in Apple's walled garden, being disallowed from installing anything they didn't approve.
Personally, I'd rather own a feature(less) phone with nothing more than a 10-key pad than own an iPhone. Then again, I buy a phone for functionality, not because "it makes me look cool".
Hint: iPhone doesn't really make you look cool, people just think it does.
Yeah, by all means, run unapproved apps and see what happens (i.e.read this article). Also, Google is closing up their source and taking back control of Android. So its not going to be "open" much longer.
Any OS is only as secure as the user behind the keyboard. Linux, Unix, Windows, OSX can all be hacked if your an idiot and leave things open.
I personally dont know anyone who bought an iPhone to look "cool" They buy it for the support, apps and games that are developed.
So basically its your OPINION in regards to iOS. And opinions are like assholes, everyones got one.