It's also about making your game accessible for as many as possible. If I have to choose between downloading a zip, unpacking it and executing a potentially malicious executable - or just play the game in the browser, I would choose to play the browser game all the time unless it's a game I really want to try out. Especially because I'm on a mac, which prevents me to play games only playable in windows.
In that sense participating in a local game jam is quite funny, because then you don't really have that "knowing your market" limitation. I've been to some game jams where people construct their own controllers with arduino boards or makey makey, which wouldn't have been possible to do in this game jam.