Not having any experience in that industry, I wonder what the driving forces of this are. I suspect it's some combination of incredibly brittle codebases that cease to build if glanced at the wrong way and aversion to spending anything on games post-release.
I am pretty sure that is the answer. Unless the game is Cyberpunk levels of unplayable, there is no money in post release support unless it is bundled with DLC or GOTY releases.
Back in the day it was pretty commonly sited figure that like 90% of a game's revenue came in the first 3-4 weeks of release. DLC and "seasons" are an attempt to stretch it out and make more off a single release, but I haven't heard how well that works.
An example that come to mind immediately is how much of a mess it is to get games that were built with Games for Windows Live like the PC port of Fable 3 running on modern Windows. It's possible, but there's a ridiculous number of hoops to jump through, none of which would be necessary if Microsoft shipped a quick and dirty update that pulled out the Games for Windows Live dependency.
- Total dependency on an engine's build system
- Lack of official support for uncommon platforms
- Extremely low expected ROI even if it were possible to deliver on other platforms
Gamedevs aren't in the business of building platforms, they're in the business (mostly) of consuming them and going where the players are.
Gamedevs not updating is because
- The engines themselves are indeed outrageously brittle at times, with LTS releases sometimes containing significant bugs that persist against newer releases of minor and major versions
- New releases can actually cause dramatic regressions, not just in terms of bugs, but in terms of features, stability, binary size, and more
- AAAs are wasting time chasing the next big thing, non-AAAs are struggling with few people and need to constantly be building the next thing because they're building products, not services
- Gamedevs are largely media/entertainment companies, very few act like technology companies
That also dates back to back in the days, we just called it expansion packs.
The primary reason is that there's no money in it. Like movies, your "one shot" game (without some sort of continuous billing e.g. mmo, subscription, continuous stream of DLCs) makes most of its revenue in the first few weeks, and once the kinks are ironed out what it makes afterwards doesn't really depend on maintenance.
Additional maintenance doesn't pay for itself, the producer doesn't pay the devs for that, and thus the devs take on the next contract to pay the bills. Not to mention additional maintenance is a risk.