There's no real evidence to suggest that bringing the game to PC would increase profits? I think you have brain damage.
Increasing revenue doesn't necessarily mean increasing profits if the cost of making it happen in the first place or a delay in future releases offsets the gains from selling on steam. It's inarguable that the game would be selling decently well on steam, it's a matter of resource allocation, training/tech and how much it would delay future releases. I can't say that that's a guaranteed win over not doing a PC port, not with confidence anyway.
That doesn't even go into the issue of whether it might impact quality of the final product if they end up sticking some poor schmuck to do the pc porting instead of working on the game itself, which would definitely have an effect. Clearly the devs don't particularly care for PC gaming either way, so even just agreeing to an outsourced PC version of the game might have detrimental effects on the current staff, if they feel that the company "is going downhill" by going on the PC. It's stupid, but you never know with creative people, they're weird that way.
I'd personally be happy with a PC port, but I kinda get why a studio of their size doesn't give a shit about it. They don't care about the money, and they seem to be happy just working from one release to another. They're basically a japanese Iron Tower only they didn't have to throw in the towel after the second game, but have been operating in this way for almost two decades. I don't know where I read it, but I seem to recall someone mentioning that Vanillaware also develops on incredibly archaic tech, which might have something to do with the lack of PC port too.
Making a Xbox version and not a PC version for a Japanese game is just pure stupidity.
From what I gather, quite a few JP devs are hesitant to do PC specifically due to fear of piracy (they're still going after people uploading ROMs of games from 25 years ago) and their work being messed with, which is a lot more difficult to do on console. In some cases there's also issues with licensing when it comes to music or voice actors. It's retarded, but the entire situation with
Takuya Kimura's agency essentially blocking a PC version of another game in the Judgement franchise, should have given everybody some sense over how ridiculously silly japanese are when it comes to PC gaming. If some of the JP voice actor agencies, for example, would keep you from making a PC port, that'd be a serious issue to be considered as you'd essentially have to chose between more sales via PC, but less star-power by not having access to the "best" voice actors. I don't know the market well enough to understand whether this is a common issue, but there are at least a few examples of studios not wanting to work with VAs that are unionized or music licence issues (we've seen that in GTA, for example).
Having your game on PC means there will be a lot of derivative work and random media using your game's assets, whether that's actual models or character designs, not to mention people could very easily make porn with it or do a plethora of other things the devs didn't intend. Devs, talent agencies or individual personalities in the JP video-game scene simply dom't wanna deal with all of that, and they think that not releasing games on PC has a significant enough impact on reducing the amount of headaches. As far as the japs are concerned, a lot of the cultural decline has come alongside the growth of pc-gaming and the internet in particular, and they wouldn't exactly be wrong either. With Kamitani being an oldschool artist, it's not too far fetched to imagine that this is a core reason behind Vanillaware not doing PC games.