I think most importantly they are paid decently. The ambitious career developer on coke or medication became more common recently, but is still an outlier and not the type to start worker rebellions either.

Smaller developers work in very cooperative endeavours. While some form of work councils don't need to be antagonistic to management, there often is simply no need of something like this in smaller studios.

Game development is an extremely high risk endeavour in any case. A large developer like Ubisoft can dampen that risk a bit, but insecurity remains. This is a large driver while they will use established formulas much more often than smaller indie devs. A union does make sense in some industries, but tariffs would probably lead to worse conditions and leave the individual dev with less choice. Currently many employers do quite a lot to accommodate devs.

The two primary motivations for building a startup are money and independence/freedom. Why would someone with that priority go and constrain themselves with the whims of others?

Silicon Valley has deep roots in individualist capitalism. You don’t get big US government contracts to design transistors in the 1950’s and 1960’s if you’re a worker cooperative. Silicon Valley was created under McCarthyism and anti-communism which also opposes labor rights movements. Since the 1980’s worker cooperatives have not been very popular in the USA, but they do seem like they would present an antidote to the worker-abusing poverty-wage paying mega corps we have today.