Programming a shitty AS2 "catch the falling object" game with the cheesiest story and uploading it to Newgrounds got me into programming. Might never have if not for Flash.
It feels like there is a desire for the same hacky frontend yet no one wants to invest.
(Disclaimer: I built it)
It currently lacks sound, but a lot of young people seem to be having fun using it to create games, animations, stories, puzzles, etc.
This: you open the page but it needs to be downloaded. You download it. You unzip it. You see that it's a Windows executable but you're on a Mac. You open it hoping that wine will run it. It does. You choose your graphics settings. You click OK. It plays.
Though I'm aware that Unity is capable of running on the web, I haven't seen that capability used much.
It is very sad what Adobe did with Flash (and Fireworks, and Dreamweaver...), especially in the wake of WASM where they could have ported most of the platform. I guess there was no financial incentives to do that.
I mean Javascript can certainly do all that but it's code first, not "IDE" first.