Flash is getting increasingly less popular. It is a phenomenal technology, and in many ways can do things with polish and flair that cannot be done though any other means on the interweb. None-the-less, as time goes on Flash use gets increasingly scarce. Here are the four biggest reasons why Flash is getting less and less popular.
Poor design by Flash Developers and Designers is the number one reason that Flash use became smaller. Remember the days when every website had an annoying splash screen with different size text sliding and scaling and tweening all over the place for about 10 minutes, until you found the "Skip Intro" thingy, located in a different place for each site? I remember them too. That sucked. And the fools that put them in place sucked, too.
Things are better today, but poor design decisions and decadent Flash usage did a lot of harm to what truly is an amazing technology. And I said "better", as in "not as bad"; so-called "flash-turbation" is not gone altogether. There are still annoying intros, or, long waits for flash to load, often for no good reason because the designer could have done the same thing in straight up HTML/CSS.
Even if obnoxious designers aren't crippling user experience with Flash overkill, there is the Search Engine Optimization (SEO) issues that Flash causes. Simply put, a Flash site acts as a near-impenetrable wall when it comes to Google's spiders indexing your site. Poor indexing translates to poor search rankings which translates to lost sales. Google and others tried to do some clever work to peer into SWFs, but the technology is iffy and will never be able to compete with snatching up the simple ASCII code that makes up HTML. That's why SEO issues are the second biggest historical knock against Flash.
But history is all about the past, and the future is now. In the past three years, two new developments have been a one-two (or make that three-four) knock out combo for Flash.
Jquery came out of nowhere, and blew every other Javascript framework out of the water. It also did some serious damage to Flash, by taking the clunk factor out of cool visual effects and transitions, often mimicking Flash animations in a way that no other JS Framework had before. All of a sudden web developers all over the world were right-clicking the cool little embedded animations and widgets on pages to see if it was Flash or Jquery. And increasingly, yup, it's Jquery.
Finally, the biggest Flash-Basher in modern times is a little outfit named Apple, run by a fella named Steve Jobs. When Jobs decided to make the hottest selling gadget of all time -- the Iphone -- browse the web without the benefit of Flash, screams of rage could be heard the world over coming from the Adobe HQ in San Jose, California. Then when Apple followed suit with the Ipad, well, things looked even bleaker for Flash.
Apple's Iphone and Ipad are what the cool kids are using. Iphone sales are approaching 100 million units (see http://en.wikipedia.org/wiki/File:IPhone_sales_per_quarter_simple.svg) and as for IPad's, well, basically IPad is the Tablet industry at this point. And neither of these two gadgets ship with the ability to run Flash.
And that is where we are today.
Like I said, Flash is an amazing technology. Even though I love Jquery, and use it frequently -- and I do not program in Flash! -- I still see a place for Flash. There are some things it can do uniquely well. But! Its role has diminished, for the reasons outlined above, and I think that does make for a better overall user experience. And a diminishing niche for Flash.