Because you have fermented them poorly and they have flaws such as fusel alcohols.
This may make you wonder: why not just ferment them correctly so they are flaw free when young? That's a good question.
Nothing wrong with aging a barleywine or RIS but if you can't make a 9% IIPA that tastes good at 4 weeks from brew day then you have a lot of room for improvement.
Ok, that post makes you sound like a total yakass...
1. Not everyone has the space, or funds, for a fermentation chamber to make something faster than it would otherwise take. There is NOTHING wrong with taking more time allowing your brew to become GREAT...
2. IMO IIPA's taste like ass covered in citric acid... Chances of you finding me drinking one that's not aged for a year, or more, is slim to nil. Same with any high IBU brew...
3. With point #1, you could need more time to get a higher ABV brew to come into GREATNESS... I'm not looking for just 'good' brews, I want GREAT ones. If that means giving it more time on the yeast, then I will. If that means aging it on some oak for a while, then I will.
To think that just because someone doesn't pump out brews like clockwork makes them a poor home brewer is just wrong.
For the record, my brews taste 'good' after just a couple of weeks, depending on what I'm making and such... But, they are GREAT once I give them more time. I'm more than willing to let them take the time to become great.
If you can produce beyond great brews in a matter of a couple of weeks, and you're not a head brewer someplace, why aren't you??
Also, for those of us that haven't been home brewing for decades, your comments are flat out insulting. Those of us that haven't been able to invest thousands of dollars in creating climate controlled fermentation chambers that keep our wort within a fraction of a degree of target are also none to happy with your comments. Saying that it's done poorly because it's not done fast is also nigh on moronic... Doing the best you can with what you have for hardware counts for more than pushing out brew...
BTW, there's also nothing wrong with giving a brew the time it needs to develop into what you really want to drink... For me, that means giving it the time it needs. Be that 3-4 weeks (for brews under "9%"), or months.
You sound like the kind of person that would also try to push out an 18% ABV mead in a month, or two, and expect it to be great and for people to fall all over themselves to drink it...