Mostly because Adobe's software updates are poorly organised.
Adobe's Downloads page (http://www.adobe.com/downloads/) is mostly about downloading product demos. Although on that page there is a list on the side with a link to the real product updates page and a very out-dated list of updates.
So then the actual Product Updates page (http://www.adobe.com/downloads/updates/) has a menu for all their products that takes you to the updates for an individual product, and a list of "featured updates". What qualifies an update to be featured is a mystery, so that list is not useful either.
They don't think to mention it on the Downloads or Product Updates pages, but there is also a New Downloads page (http://www.adobe.com/support/downloads/new.jsp) which is actually rather handy, although there is no indication what constitutes "new" so it can be difficult to tell if something was released in the time between your last visit and the oldest update mentioned on that page.
My favourite aspect of Adobe's support pages is the whimsical approach to the page for a product. For example, the page for Illustrator for Macintosh (http://www.adobe.com/support/downloads/product.jsp?product=27&platform=Macintosh) includes the 15.0.2 update for Illustrator that shipped as part of Creative Suite version 5. Meanwhile the Creative Suite for Mac updates page (http://www.adobe.com/support/downloads/collection.jsp?collID=1&platform=Macintosh) doesn't admit there have been any updates for CS5 at all.
Updates for some products (notably Flash) are missing because all this works by heavy-duty screen scraping and Adobe likes to keep you guessing by having totally different page structure for some products (notably Flash).
There is also the problem of meta-products like Creative Suite. I have some scaffolding in place to handle it but the trick is to have robots work out when to include an update in a meta-product. In my defense Adobe obviously thinks this is a toughie too.
I did investigate the built-in software update service used by Adobe's apps, but couldn't see a clean way of determining what the required keys will be for products I haven't witnessed phoning home.
The encoding is broken for some of the text. But then the encoding is broken for many of the product pages on Adobe's site. Garbage in, garbage out. AND EVERY PAGE CLAIMS TO BE XHTML JESUS.
I hope to improve how the screen scraping works. But if you still want to complain please contact me via e-mail.
Please direct questions to David Buxton <firstname.lastname@example.org>.
If you are Adobe then of course I will take all this down just as soon as you say so, but you should think long and hard about whether you wouldn't prefer to wait until your support site is less hostile. Also publish an Atom feed of recent updates. Or if you really want to sell it to the marketing guys, tell them you will have a bot that tweets each new release (in addition to the feed). Those hippies in marketing love Twitter.
Updated 5 December 2012