The people making games, applications, and lush webGL marketing demos are people who can throw lots of engineering resources at a problem until it does the thing they want it to do. Web dev has always been an insane mountain of hacks in order to get pages to render, but the attractive and democratic reasoning is that that extra effort is worth it if the maximum number of people can access the information. People on old computers, cheap smartphones, kindles, chumbys, whatever. The best computer is the one you have on you, that sort of thing. Access and ease-of-adoption are powerful things.
No amount of java applets would have ever made up for that.