"Why would they close the doors?"

Very good question, but one that needs a responsible answer. Adobe wants the web to live on using its proprietary formats like Flash while a growing minority is resisting this and switching to HTML5. Adobe's efforts are a good start but have a long way to go. Muse, for example, has good intentions but in practice is a horrible product with extremely convoluted code.

I'm not a Flash hater as I love the fact that YouTube grew on this standard and many fun games are because of Flash but I also see the reason why HTML5 is a much better standard to get behind and why technologies like Flash will ultimately die unless they become more open.

You have to understand Adobe's view of Flash. The reason they were pushing so hard for Flash support is that they wanted to be the gateway to multimedia and interactivity on mobile devices. For the longest time, Flash was how you played video on the web, and Flash was how you made rich, interactive websites. When iOS came along it threatened that, and Adobe wanted to protect their stranglehold in order to maximize their profits (e.g. of Adobe's flash content creation tools).

They've now realized that this isn't going to happen; people are abandoning Flash Player in favour of more compatible, more nimble technologies. Adobe's a big company, but they know which way the wind is blowing, and they've responded by shifting with it.

The way things are looking, 'Adobe Flash' (the content authoring tool) is going to move to being an HTML5-and-fall-back-on-Flash-Player tool (or vice-versa). Eventually, Flash Player will die the death it deserves, and 'Flash' will just be the name of the authoring tool (along with Dreamweaver or Coda).

Basically, Adobe wanted to lock up (or at least make a lot of money at) the cross-platform mobile dev environment. They realized they can't do it with Flash Player/swf content, so now they're trying to do it with Phonegap Build and HTML5 content. More power to them.

Sadly, Flash still is how you play video on the web and make a lot of rich, interactive presentations on websites b/c only in the last few years has HTML5 started taking off. We're stuck in a proprietary world until we get over the bickering and complacency of open standards.

I'm definitely not trying to discredit the HTML5 work Adobe has done to play catch up but part of me feels like it's too little, too late in some ways.

Adobe has to make money, they obviously have a huge grip in the design community and they're not going away anytime soon so we need to push back as much as possible to make sure they don't continue on with bad practices and listen to the community, which increasingly they are. Sadly, too many of us feel abandoned when some of our favorite software gets left behind (Homesite) or bloated (Photoshop/Flash/Illustrator).