So this is something I'm curious about. When the Vita came it out it bombed. It bombed pretty hard. Nobody was developing for it outside of a couple exclusives from Sony released each year. In Japan every 3rd party was flocking to 3DS in the beginning. Games were getting announced for that platform left and right. And then on a dime, everything changed. For some reason the Vita started to get a ton of Japanese support. To the point where it was getting most of the mid-tier and small-tier releases. Sure the major franchises like Dragon Quest and Monster Hunter stayed on 3DS but what about everything else? Toukiden, God Eater, Demon Gaze, Hatsune Miku, Persona 4, etc. all saw releases on Vita. Why not just put everything on 3DS? That's what they did with the PS2. Nobody was clamoring to put games on the GCN. It got to the point where the Vita actually managed to build a respectable install base in Japan and continues to get regular releases. 

So what happened? Was it just good old Sony loyalty? Japanese pubs still mad about Nintendo's scummy tactics in the 80s and 90s and now they're getting some revenge? 

Its blackmail. Sony has revealing information about the Japanese 3rd parties that would be damming to their enterprises if it were to come out.

Look for continued Vita support.

Well, one thing that comes to mind is power: a lot of Vita releases are PS3 ports, so there's no way the 3DS could make them. Other genres can develop a decent and loyal installbase on the Vita, and the PS+ service guarantees a constant consume of new games, so they're profitable even with smaller prices.

I wouldn't say they "saved" the Vita, but they helped it a lot. If it wasn't for them, Vita would be selling like the 360 right now. I think they gave it a chance because it was the perfect platform to realize their niche games. Notice how big japanese games, like MH, FF, DQ, Yokai Watch, etc. never appeared on Vita.

Because they knew/know the potential of the Playstation Vita (PSP was a huge success in Japan) and wanted to creat games which were/are not possible on 3DS (Soul Sacrifice, Freedom Wars, Toukiden...).

360 numbers? This is impossible for a Japanese console! 

Here are the options for Japanese third parties right now

1. 3DS - Leading plat form, but it is weaker and competition is stiff with major IPs (Monster Hunter, Pokemon, etc.)
2. PSV - Secondary plat form, stronger and easier to do cross platform titles on PS3 or even PS4
3. PS4 - Despite success in the west slow to transition to new system, 2015 and 2016 will likely see the shift happen
4. Wii U - Poor sales world wide make the system not that appealing
5. X1 - Dead in Japan and demographic of western owners don't help either

Of course...then there are phones which is the real #1 in Japan.

So, when you look from their view the Vita isn't a big risk and many companies have found success on it. Especially given Sony offers little competition in software so it essentially is a third party system.

Vita equals PS3 port, which is something developers just started to get a hang of by the end of the PS3 life time along with being the cheaper option for the strong Sony fan base in Japan.

Also as succssor to the PSP, it is home to a bunch of more PC like games such as visual novels and more indie affairs. So while the 3DS may sell more systems, the Vita offers the ability much like the PSP did for PS2 developers, to use older and now cheaper development tools and a built in fanbase that links to the PSP.

Honestly, Japanese publishers screwed over the Vita at the start by continuing to make PSP games instead of moving to the Vita. In general, they're a pretty short-sighted lot.

As I argued a couple of years ago, though, working to build an alternative market is a good thing. Japan needs both, or you'd see a situation where lower-tier games would absolutely get buried on release by the big names. Honestly, if you're a small developer with a new IP, which console is more attractive? It depends on the demographic, of course, but I would imagine some IP will perform better on the Vita.

They haven't really saved anything, big third parties like Capcom, Konami, and Square-Enix still generally avoid the Vita like a plague, giving it token support at best. It won't come close to sniffing the PSP's LTD in Japan.