Personally I don't understand how next-gen only expansions are greenlit. You're already dealing with a much smaller audience, as the add-ons will usually only interest those who finished the game or at least made signifcant advances. Now you're also removing the players with past-gen consoles from the potential list of buyers...
They do the math and can tell where their audience is. And then, they take the financial risk.
- In the case of Horizon, for example, a reported 70% of the game sales were the PS5 version. (There are a lot of PS4s still out there, yes, but many are collecting dust, having either been replaced by a PS5/PC or else just forgotten by the buyer over time as their hobbies changed.) If there's only that many people buying on PS4, and assuming a percentage of them are not hardcore gamers anyway who would collect DLC even though they bought the base product, you can project your sales and plan accordingly. So for Horizon, they planned early enough that they could tell the effects and technology they were introducing in the DLC wasn't worth even trying to port down to PS4. (Not that it would have been impossible to figure out some solution, but Guerrilla is already a key tech driver for Sony and so spending more time making clever work-arounds for PS4 solutions isn't a good use of their time when they could instead be working on RTGI and other advancements for future titles.)
- Phantom Liberty meanwhile was just a throwing up of hands, writing off the PS4/One versions as the best that could be done but the future was on the platforms this should have been on in the first place. Past-gen consumers got the product they were expecting (more or less) and weren't promised a long tail of DLC content so it what it is for them; if that audience complained about not getting DLC, fair enough, but nobody heard them over the rejoicing of those who had the hardware that Cyberpunk would thrive on. (And again, the publisher had the numbers. We don't, unfortunately, as platform breakdowns are hard to find and even the Horizon info is not confirmed, but the trends in platform support are clear either way, that PS4/One are being left behind even in games which clearly could have been ported down and in fact have Switch versions on that side of the tech tree.)
- Intermission and FF7 Remake is a weird one. You would think Square would continue to support PS4 since PS4 is still a big market in Japan and is where a lot of these cross-gen releases are still coming from. (Plus, I'm not sure most Japanese apartments can fit a gigantic PS5 inside...) Also, there's no clear infusion of new tech on Intermission or FF Rebirth over Remake. (Both are still UE4 rather than a new engine, and we don't know the PC specs for FFVII Rebirth but FFVII Remake Integrade PC has Intermission yet isn't in that next-gen-only spec range.) It seems like they simply committed to a marketing plan (again, by the numbers, although I'm not sure what numbers they would have since Remake shipped so late in the PS4 lifespan, the PS5 was almost out by then... Forspoken sales wouldn't have been enough data to make such a bold choice IMO,) and locked into a current-gen-only sales plan. Surely FF fans will show up no matter what, so if the PS5 install base is big enough to support FFXVI, it's big enough to be the only place to get FFVII Part 2.
Just wait until a new sequel if you want to make a bigger leap.
As nice as it sounds to current-gen owners that their hardware is getting special treatment (and as much as past-gen owners might grovel over being left behind, they must know that this is the way with hardware gens, that the future is on the new devices,) many of these decisions aren't being made for "a bigger leap".
Mostly, it's to save time and resources, as well as to cut out SKUs in QA that are unlikely to sell much.
Even with Horizon, sure, they got a great cloud system in there and were able to design around open flight much more confidently, but I would imagine they were planning all of this for both versions, and when the math came down that PS4 was a waste of time going forward, they let out a sigh of relief that they had one less annoyance to deal with. Going PS5-only let them do some things that gamers would consider "a bigger leap", so that was a nice bonus bulletpoint to sell the DLC on; it also let them try some new stuff that they couldn't get in the main game's production schedule, sort of like Frozen Wilds and the PC port, which would help them in future versions of Decima and Horizon. Win/win for going next-gen-only, with the only downside being that whatever percentage of PS4 gamers were upset. The DLC itself, however, was probably not greenlit on being "a bigger leap", it was just the planned extra content piece for this Horizon sequel and timing/marketing just worked out in the PS5's favor.
