I think rather it's a revenue issue, until relatively recently there was no way to profit from updated games, so you're better off moving on to the sequel, or next year's edition of the game. Also a lot of the video game development culture likely stems from console releases, which again until "recently" could not be updated (only new versions of disks/carts for future customers) so it was not feasible to plan for future maintenance, beyond what was necessary for derived codebases.

it's a hit driven industry, so maybe the dynamics are pretty startup-ish: you don't know if the product is going to take off, so cut corners to reduce costs in the short run at the expense of future maintainability, since you don't know if the product will be profitable and have a future until after it ships.

if the product is wildly successful and has a future, but is a bit of maintenance nightmare: congratulations, that's the problem you want to have