On the other hand, the browser provides a ubiquitous, consistent-enough runtime across basically every consumer computing device, and people who are interested

On the other hand, the browser provides a ubiquitous, consistent-enough runtime across basically every consumer computing device, and people who are interested can get up and running with developing basic apps for it in a matter of days, using only tools that cost zero dollars. Can you imagine what the designed-by-committee-for-that-purpose version of a universal runtime would've looked like? (hint: the answer is it looks like the Win32 or Java platforms/APIs and has just as many warts if not more)