It's both. It's good to support the platform with games, but it's nice if u make money with these games. Xbox exclusives hardly are any kind of blockbusters so PC version is wise. 

If the port makes a profit, yes.
If it doesn't, no.

It's pretty simple.

No its sellong ok on xbox.

A port is very easy and inexpensive because the hardware architecture of both systems (AMD64) is nearly identical.

Kingdom Hearts is a big game, the first 2 main games sold 10.7 millions(Vgchartz numbers) combined.

Nope, looks like it did pretty ok on Xbox.

Doesn't matter really if they made there money back it's all great.
I Expect PS4 version to be at least 4-5 mil life time
Xone version will be 1.5
And when they release it on pc it will sell about 500-1 mil copies so i think Square is good.

easily worth it. it sold 450k in the usa alone in its first month.

Just go ps4 only at launch with a pc release 1/2 years later. A large chunk of the small xb1 sales will get it on ps4/pc anyway so you really aren't missing out on much.

If Microsoft paid for the xb1 port then I'd give it to them.

Yeah, it was. Sales aren't nothing to light the charts on fire (450,000 units sold, if I am not mistaken), but that also gives indication of legs (wouldn't be surprising if it makes it to a million), and already beat other games which arguably were less worth to port, given sales, like FF Type-0 HD. 

Considering that porting these days is much easier, this version is doing fine so far.