The-Nastiest
Newcomer
This has been an economic reality since console generations became a thing, though. It wasn't ever a hinderance enough to stop development of next gen only titles, until maybe now. Honestly, I do believe that Microsoft coming into this gen with a "cross-gen ride or die" attitude was both seen as pro consumer enough to win some good will, and that the underlying technology of modern games is usually scalable enough to hit both targets with a playable experience.
To be honest, it isn't like sales of next gen only titles have really suffered, have they? Rift Apart moved a million copies in just over a month didn't it? A quality game will do that. There are also plenty of examples of quality software released on last generation hardware selling poorly. That's why games like Megaman 6 on NES and Shante on Gameboy Color cost so much now. Because nobody bought them back then. Shante is a prime example, because GBA would have played that via BC. I'm sure there are example of PS1 games or PS2 games that fit that bill as well. Rule of Rose comes to mind. There is a risk in not making your game for next gen as well.
While I agree that it's been an economic reality forever, the ballooning cost of game development has changed. The amount of copies to break even or make a profit is higher now than before and probably hasn't scaled linearly with how it was in the past.
Even in your example of Rift Apart we know it sold at least 1 million copies, but in a vacuum as a singular release by a sole developer, what was the break even sales number for a game that had such high production values? Well, we don't know that, but what we do know is that Insomniac can take that risk. Their business team can justify it since the single platform, next-gen only Ratchet was sandwiched in between a Miles Morales release on PS5 and PS4 and then Spider-Man Remastered PC and another Miles Morales release on PC (have we found out if PC players have to pay full price for MM even if they bought Spidey Remastered?).
So even if Ratchet missed goals, the very popular and well selling Spider-Man games were going to support any potential shortfall.
They were able to take that risk.