The expensive and mandatory Proprietary Memory cards definitely did not help with matters.
Sony stopped making games for it and the only support it has now are Japanese titles. Japanese titles, while successful in Japan (obviously), are for the most part niche everywhere else (of course there are exceptions such as Final Fantasy).

Lack of advertising did not help either.

3DS software sales do not reflect its install base in the West. Parents bebuying their the hardware, but so the barring odd title.

Handheld is much inthe west regardless what the install base says. You need look most shops see that.

i read on budgetgamer.nl that the Vita isn't even available in most stores anymore in the Netherlands.. online only 1 webshop has it..

Nintendo Dominance + Smart phones + media banging on about it having no games = disappointing sales.

Not everything looks bad compared to the 3DS (PS2).

For the price, didn't the 3DS get a $50 price cut like 3 months after release? Sales got boosted 2 or 3 times thanks to new revisions. So, while 50M sounds good on paper, lots of things had to happen to get to that number (early price cut, multiple revisions in quick succession, MH).

I think the fact that Nintendo is going mobile and merging their console/handheld says it all.

No games outside of rpg's, made me get rid of mine, and get a 3DS XL, instead.

People who say PS Vita had a bad support from beginning are stupid tbh...
It got a great support in the first year: exclusive Uncharted, exclusive Call of Duty, exclusive Assassin's Creed, exclusive LittleBigPlanet, exclusive Resistance and much more great stuff like Persona 4: Golden or Playstation All-Stars Battle Royale. And don't forget the great third-party games like Need for Speed, Mortal Kombat or Metal Gear Solid Collection. So people didn't buy PS Vita because there are no games? Seems legit...

Imo there are 3 reasons why PS Vita sold badly:
1. Bad advertisment
2. Smartphones
3. Bad memory card prices

The exclusive Call of Duty game was critically panned, which is a big deal considering Call of Duty usually has very good reception.
The exclusive Assassin's Creed title did not stay exclusive for long, in fact you can get a copy on the PS3, 360 and PC.

A lot of the good games that third party developers released for the Vita were console ports. Most people who want to play those games who are Playstation or Xbox owners would get those games on their home console instead. The Vita needed more games to set itself apart. 
There is nothing wrong with the Vita, don't get me wrong. However, Sony and Western third party developers simply did not do the platform justice.

The smartphone market took a big chunk of the hadheld market, and Vita´s price is too high for a portable console (specially due to the mandatory use of Sony memory cards).
In my country, shops still sell the Vita, but it´s so expensive that people always end getting a 3ds instead. As for games, it is getting increasily more difficult to find.

People buy consoles and Handheld for AAA games