Well that is the lightning in the bottle element. Having a solid success from your game, sure you might expect that. Your game making a billion dollars, winning every award out there, and changing the scope of the market.....that is not something that always happens even if you work hard and plan for it.
I just don't really think it is. The market is ever-expanding (for now). When you spend money on quality work, and present an RPG that's accessible and not very challenging conceptually (the most challenging element being turn-based, honestly, but that's still wildly more popular now than, say, 5-10 years ago), people buy it, because the market is nowhere near saturation. We'd probably have to release 2-3x as many AAA RPGs per year to hit saturation (whereas shooters, for example, esp. competitive multiplayer ones, are wildly over-saturated). Maybe they couldn't have "counted" on $1bn, but they could have "counted" on probably $400-500m.
I'm struggling to think of any AAA single-player RPGs that genuinely "worked hard and planned for it" which weren't massive successes - indeed most kind of commensurate with their budget or better. Can you think of any? That just inexplicably flopped or done "mid numbers"?
The only way to avoid this is to really make a huge effort to screw things up.
Cyberpunk 2077, for example, rushed to release, and had failed to address the wild and unrealistic beliefs gamers had about the game. It'd have got away with that, though, if it wasn't for releasing on older consoles in a version which was barely functional and insulting to customers. Even then, the core of the game was sufficiently solid that it sold 13m copies early on. It's now over 25m sales (and sold 5m copies of the expansion DLC nearly instantly when that came out - quite deservedly - it's an incredibly DLC for which they did "work hard"). That's incredible sales, and it's because it was basically a really good game they just messed up a bit on. Even at 13m copies it sold it had a huge profit.
Starfield did underperform, but it was obvious that it would, and had been obvious for some time, and they hadn't "worked hard" nor properly "planned for it". That was the entire problem. The game is a half-arsed outdated-feeling mess that's lazy on literally every single design and conceptual level except maybe textures. 7 years of resting on their laurels and deciding that junky systems, and poor design, and more repetition/reuse of maps than Dragon Age 2 were "good enough". People attempted to defend it, but what a mess. In fact the biggest problem is it was defended so extensively by some fans and even some critics that I'm not sure BGS will actually learn a lesson from it. People love to say "Well Creation Engine is fine", but no, it isn't. They had to drop many of the coolest features of the engine (like people having proper day-behaviour cycles and travelling and so on) because the engine is creaking too much, and they clearly could not just upgrade the engine enough to look good, feel good, or even play good. It did pay for this and especially for being available for "free" on Game Pass and has only sold like 3-4m copies to date.
Mass Effect Andromeda failed for somewhat related reasons - they didn't plan and they didn't "put in the time". They were basically making No Man's Sky before No Man's Sky before they were told, "Nah, kick it out the door!" by Aaryn Flynn, who wanted everyone to come and work on Anthem full-time. So apart from the art assets, the entire game was developed in 18 months. Further, it had a $40m budget, which was a fine budget for an AAA in 2007, and okay budget for one in 2010 or 2012 (ME1, 2 and 3 respectively, which all also had $40m budgets), but was pretty pathetic for an AAA coming out in 2017, especially spread over 5 years of development.
Now in the AA sphere things are a bit different. Where budgets aren't as high, things aren't as guaranteed, and you can't provide the same experiences that bring people to AAAs. But that's not where BG3 was ever operating. It was always a high-budget AAA.