I think it depends on how you define fun. For me personally, does a workplace need to have alcohol, video games, bowling alleys, and ping pong tables? Probably not. It does need to be interesting though. And my co-workers/team need to be enjoyable to be around, both professionally and personally. If I'm not consistently having a good time at work, which could be construed as having "fun", there's very little reason for me to stick around. Especially in the tech scene, there's always a better place to work, so it's competitively advantageous for companies to have "fun" workplaces.