Why do people claimed only Nintendo games sell on Nintendo platforms as if a bad thing?

[binary solo]

Highest selling 3rd party titles vs Nintendo titles on the last few Nintendo Consoles.

Wii: Just Dance 3 = 9.3 million vs. Mario Kart Wii = 32 million (didn't count Wii Sports because of it's autobundling). Ratio 1: 3.7

DS: Cooking Mama (O_o) = 5.35 million vs NSMB = 28 million. Ratio 1:5.35

Gamecube: Sonic Adventure Battle 2 = 2.56 million vs SSB Melee = 7.07 million. Ratio 1:2.76

N64: WCW Revenge = 2.38 Million vs Super Mario 64 = 11.89 million. Ratio 1:4.99

GBA: Namco Museum = 4.24 million vs Pokemon Ruby/Sapphire = 15.85 million. Ratio 1:3.73

Average ratio 1:4.06

The other company's consoles?
Sega being a strong 1st party producer has similar ratios between highest selling Sega game and highest selling 3rd party.

Microsoft, probably expectedly, has it's Halo franchise be the highest selling games by a long way on XB about 1:2.5. But the situation is reversed on 360 (I don't count Kinect Adventures due to autobundling). But Halo aside MS really doesn't have a strong 1st party stable like Sega and Nintendo.

Sony, again with PS, like XB it's first entry into consoles lead with 1st parties, albeit the difference between Gran Turismo and FFVIII was ~1:1.5 so a very low ratio. And while technically FFVII was first party (published by SCE) it wasn't really so arguably the ratio is even lower than 1:1.5, and FFVII was the #2 all time PS game. PS2 and PS3 though have 3rd party games as unarguably the best seller despite having substantial 1st party titles, and good quality titles too. PSP alsp followed the PS2 and PS3 pattern, even though it was Sony's first entry into hand helds. I get the feeling that PSV will heavily favour 1st parties, but not for positive reasons.

So in some respects really strong 3rd party sales compared to 1st party is a recent phenomenon, even an exception to the rule. Still I expect for Sony and Microsoft leading 3rd parties will be the norm for however long they stay int he game. But Nintendo will always lead with its games,

What makes it bad from the Nintendo perspective is that Sony and Microsoft will always be able to attract significant 3rd party support, and so, at least in home consoles Nintendo is unlikely to ever achieve the massive dominance (>50% market share) that Nintendo fans seem to want so much. But other than for bragging rights purposes leading with 1st party titles seems fine.