Spolier: Do not put 'listening to leftists' as your answer, too easy.
With the paracite hangers on of game 'journalists' the first to go, the amount of bleakness from Ubisoft, EA trying to sell itself harder than a crackwhore, we are approaching a point where we may end up with only 3-5 major ones left and a few focused on one title that's been around for decades (eve online, your DOTA games etc).
Doesn't really affect us as I think I'm safe in saying we all have backlogs that can outlast us being on Earth! So why not make this a fun opportunity to go 'you know, if you did this , you wouldn't be begging for money'. Choose whichever companies you want on what you think was a missed opportunity:
EA: Not using their IPs together enough. Seriously how hard would it have been to make a Battlefield game set in the Command and Conquer Red Alert or Tiberium franchise or even do a sports game but in the backdrop of Mass effect. They seemed to be all about processing IPs than using them effectively.
Bethesda: not using an Id engine for Fallout 4. When I played Rage, the story was lackluster but the combat and gameplay was smooth, fun with fantastic visuals. Unless there was a hidden licensing reason, why not use THAT for Fallout 4, that seemed like the perfect engine .
Nintendo: making it too difficult to buy and play older titles so creating a piracy market.
Microsoft: not letting gamers be the one to design their military AR project as they could've probably told you the dumb parts quickly.
Sony: Not embracing Japanese game devs, not leveraging their monopoly on anime with PS+ by doing, for example, free first 3 episodes of a series on Crunchyroll if you have PS+. Also on Crunchyroll, just put an adults only section for uncensored anime, have it behind a paywall of some small fee and a SECOND password and you'll probably get a lot more subscribers.
There's more I could mention like Ubisoft, Rockstar, CD projekt etc but gone on too long and let this be a collective 'I would've done this' thread.
Gonna avoid the low hanging fruit for a second and say: this started with the melding of console and PC game engines. This is why, for example, Microsoft killed 3D audio on Windows after the XBox came out - the Xbox didn't support such things and they wanted a uniform framework for both platforms. Let it sink in that PC game audio 20 years ago was more advanced than it is today. Today, PC games are usually just console games with minor tweaks. Real antialiasing doesn't even exist any more thanks to shitty deferred rendering engines and lazy programmers who don't want to put more effort into supporting something only PCs can do. The games themselves have also become artistically bereft and generally designed for knuckleheads.