Right now for software development as a whole, unionization isn't necessary - we (if I'm allowed to speak for others) aren't exploited, forced to work 80+ hours / week, underpaid, etc. Generally speaking.

Game development however is a whole different ball game. The problem with game development is that there's a TON of people that would love to do it (because they love games), which makes for an easily exploitable labor force. Don't want to work 80 hours / week? Fine, everyone else does, and there's ten others that would love your job.

Of course, this is about the US which is also lacking in basic employee protection laws. The US is teeming with active cases of slavery (prison workers, unpaid overtime, sub-minimum wage payment to be stipended with tips, easy to fire people at very short notice without any compensation, etc), and no unions are around anymore to stand up for it - because companies can afford to fire anyone trying to, and there's plenty of desperate people to fill in the ranks. Free market.