P4’s GUI/model is also intuitive for non-programming roles to learn and use historically compared to git, so a team with wide skills can ramp up quickly with a unified toolset. A less-technical manager gets a GUI that has versioning across changes from a multidisciplinary team. You can probably guess what inertia that has in a space with higher turnover compared to other industries.
As mentioned, things are changing though. git and GitHub have become a mainstay and are what new programmers likely learn in schools. This has a trickle effect on new projects with smaller teams and results in more investment into git setups. I use git in a AAA context at work, and it’s not uncommon to find sentiments from more seasoned game programmers on git that are similar to HN comments about the latest fad in web frameworks.