The difference is, that even though Flash was proprietary in tools (The Flash IDE) and the playback engine (The Flash Player), what was open was distribution, d

The difference is, that even though Flash was proprietary in tools (The Flash IDE) and the playback engine (The Flash Player), what was open was distribution, discovery, and marketplace. You didn't pay a tax to adobe to distribute your games and you weren't limited to Adobe.com as the one place to go for Flash games. To be clear this was not because of Adobe's benevolence, but their incompetence -- believe me they tried to find ways to tax Flash, but they just couldn't figure it out until the horse was out of the barn. And this was a good thing for the ecosystem. Honestly, Adobe stubbornly refusing to open source the flash player is one of the things that cemented its demise. Compare that to say, Roblox. If you make a Roblox game, not only will it only run within the Roblox environment, it is only able to exist on exactly one website and one app -- Roblox. Roblox owns the entire stack top to bottom. You can't take your game anywhere else.