When you list the portable games as well you see that they're releasing a lot of games each year.

why don't sony or microsoft make more games?

the reality is 3rd parties is what make consoles shine. Without them there is droughts.

And what should that be? On the one hand, their handheld systems have a higher userbase. On the other hand, their consoles also have a respectable fanbase and are more powerful than the handheld systems which allow for newer experiences with games. Also, in their best years, the DS sold like the PS2 while the Wii sold like the PS1. Let's say NX is a home console and it's a huge hit like the Wii was. Do you realy think Nintendo is stupid enough to alienate tens of millions of petential handheld customers? The problem is you have Nintendo customers who will buy a Nintendo console and not a Nintendo handheld while you have a lot more of their customers who will buy the handheld and not the console. Nonetheless, Nintendo's customers expect both.

Satoru Iwata actually addressed this problem in the past and hinted that both Nintendo's next console and handheld would be sharing a unified archetecture which would make ports easier and allow for quicker development times accross multiple platforms. Given that Nintendo's console and handheld hardware teams were merged into a single division a few years ago, this is most likely the direction NIntendo will be heading in.

That brings one other issue up. NIntendo develops more games in a given year than just about anybody. I pointed out in another thread that between November of last year and may of this year, NIntendo released about 11 games, the majority of which were on the Wii U. That is insane. Name one other publisher who's capable of doing that. Nintendo's problem isn't that they don't release enough first party content. It's that they don't have enough third party support on the Wii U. The 3DS can get away with few first party releases. The Wii U can't. 

This is why Nintendo is unifying their handheld & console. Here is Nintendo 1st party titles just this year

The Legend of Zelda: Majora's Mask 3D
Pokémon Shuffle
Kirby and the Rainbow Curse
Mario vs. Donkey Kong: Tipping Stars
Codename S.T.E.A.M.
Fossil Fighters: Frontier
Mario Party 10
Boxboy!
Xenoblade Chronicles 3D
Pokémon Rumble World
Stretchmo
Puzzle Dragons: Super Mario Bros. Edition
Splatoon
Dr. Mario: Miracle Cure
Art Academy: Home Studio
Super Mario Maker
Animal Crossing: Happy Home Designer
Yoshi's Woolly World
Pokémon Super Mystery Dungeon
The Legend of Zelda: Triforce Heroes
Star Fox Zero
Mario Tennis: Ultra Smash
Animal Crossing: Amiibo Festival
Xenoblade Chronicles X

On top if that they also fund games like Devil's Third & Fatal Frame V: Maiden of Black Water and help with localization of games like Little Battlers Experience & Yokai Watch.

The output is fine, the problem is that it's spread out across 3 separate devices.

Pretty much this. You can combine the list for handheld and console and combine them across Wii U and 3DS and you would swear it was one of the most impressive lineups in gaming history. But because its so fractured it makes the lineup look sparse. NX will fix this and then some. I bet that some people will be complaining that there are too many Nintendo games next generation.

They thought Wii U would be successful without big games, only because it is has the Wii in its name.

Nintendo doesn't have too many employees, but unifying their systems should take care of this issue.

It is partially the fault of their hardware engineers though

Actually agree with this, but the lack of variety and new ip that surpase the old ip is still below below other competitor, The actually made a lot of games but same ip over and over again will look like they have small amount of games , and also Wii U lack of 3rd party support make it even worse.

Because mismanagement. They delay games that have already a lot of development time while rush other ones to fit certain schedules.