Is it because Nintendo games can't sell on other platforms?

Third parties try to use it as a (pathetic) excuse as to why they don't put their games on Nintendo systems. They think they can't compete.

envy

Because your grammar is terrible.

'cause it's too bloody kiddy for their eyes... :I

Grow the hell up with that grammar nazi crap and just correct him next time.

People want to enjoy Super Mario Galaxy. People want to enjoy Super Mario Bros. People want to enjoy Super Smash Brothers. People want to enjoy The Legend of Zelda. People want to enjoy Donkey Kong. People want to enjoy Metroid. People want to enjoy Star Fox. People want to enjoy Pikmin. People want to enjoy Mario Kart. People want to enjoy F-Zero. People want to enjoy Pokémon. People want to enjoy Fire Emblem. People want to enjoy Kid Icarus. Heck, some people even want to enjoy themselves some Wii Sports.

But along with that they also want to enjoy third party titles, which is why they consider a Nintendo console purchase a waste.

You're right. I apologize for my stupidity.

It's usually thought by 3rd parties, because it means that their own games can't sell on a Nintendo platform meaning that they can't make a sale on a Nintendo platform.

But it's as Rol always said, it's proof of their incompetence.

I think that for this generation at least a lot had to do with the fact that 3rd party developers could make one multi platform game which could run on 360/PS3/PC while they would have to make a unique Wii version due to far less capable hardware. It simply wasn't cost effective.

Consequently the bulk of development resources were dedicated for those platforms and the Wii was left with the scraps so to speak. All of this leads to a situation where most 3rd party games are perceived to be "inferior" on the Wii even when motion controls are used effectively.

To answer the OP more directly I would say that people saying only Nintendo games sell well are misinformed but only to an extent. While it is true that Nintendo 1st party games sell the best overall, there have been some successes by 3rd parties as well. Of course this pales in comparison to how well they perform on the other consoles and this is what most people focus on.

Hopefully Nintendo learned its lesson and will at least provide a comparable console to the 720/PS4 otherwise 3rd party support may turn out just as bad long term.