It's more to do with HTML5 than lack-of flash, although it could be argued that flash's long-prophesied downfall was one of the reasons for HTML5's rapid adoption.

HTML5 is when the web stopped being the web. It has no legitimacy in calling itself "hypertext", it's an app-delivery mechanism with a built-in compatibility layer. In this regard Flash is just as bad and probably even worse, but since it wasn't in anyway standardized or even open-source there was a fair amount of pushback from all fronts. HTML5 had no such pushback.