Why? You haven't made any a slightest attempt of an argument putting forth why you think that is. What is it about Catherine that would make a port troublesome?
Or are you stating that any game under X copies is not able to pay for its port cost?
Again, I don't know how much the actual cost of porting the game is. I am guessing it was a bit troublesome to port since the original game was on the Gamebryo engine and the Vita port isn't but for all I know the porting process might have been very simple (if anyone knows some additional info about this, please chime in). But 10k copies worldwide is not a lot. Like for example the Ys VIII also sold only about 9k LTD and if this was a Japan-only title I would also be saying the port was a flop. But it sold very well overseas, so it was worth doing. Right now we are looking at about 74,000,000yen in total sales. That is under $700,000 US.
Catherine Full Body was announced in December 2017. That's more than a year ago. Let's assume a very small team was in charge of porting it. Let's say 3 people for 1 year. And let's say that they were paid only 33k a year (which is pretty low). There is $100,000 right there. Ok now let's add in the cut Sony takes, the cost of the Vita cards, packaging, shipment costs, retailer cut, etc. To be generous let's say they still had a profit of $400,000. Opportunity cost is a thing and the time spent on this version could have been spent on other things. And notice how I am not saying that Catherine Full Body itself was a flop. The PS4 version has overseas sales potential and more than likely already covered it's costs with (5x the sales of the Vita version)
I do not work in the video game industry, so I am willing to concede that I could be wrong. But until I hear from Altus or someone with insider info, I stand by Catherine Vita being a flop.
And yes Nobunaga's Ambition for Switch is also a flop since it is not getting ported outside of Japan. Though as
KtSlime already mentioned it is built on an engine they already had on Switch, so my guess is, it was an easier port.
