Games get cancelled, often before being announced.
It seems "abnormal" for some about Retro because there's more scrutiny about them, and because they're the only major western studio for Nintendo, despite it not being "big" at all in terms of headcount.
It's certainly not unusual for the same thing to happen for other studios, you just don't notice it or hear about it because they're teams/divisions in way bigger studios (EA/Ubi/Capcom...), and in a different organization. Rocksteady's new game hasn't been announced for example, and will release 5 years after their previous game. Retro has been put on a major title since only the beginning of this year, and it's a development reboot situation. Their previous project could have been cancelled because it wasn't interesting in the end, because they (or nintendo, or both) chose to work on MP4 instead, because it was going nowhere, etc. Good project management is also deciding when to kill a project (and not wanting a second Project Hammer).
People have a weird obsession with "what could have happened there?!" for Retro.