Because it's really cool to try out experimental instruments other poeple have made by simply opening a webpage, without having to execute untrusted native code that could have bad consequences.
I'm interested if this is true. It seems like the js sandbox is pretty well implemented now in most cases. Webgl had some problems at first leaking host data, but the willingness to sacrifice performance for security seems pretty ingrained in these consortiums?
You oversaw the untrusted part, this is the only reason I prefer web over native really. If there was a way to run native apps with that level of isolation, I would prefer native.
Unfortunately, none of those are cross-platform... Closest we get to something similar to the web is either the JVM or APE (Actually Portable Executable) but then those are generally not as isolated as the alternatives you mentioned, sadly.