Inform yourselve first before making baseless assumptions op. Nintendo actually makes quite a decent amount of new IPs on a regular bases, on top of that they have a large amount of successful IPs a lot of people actually want sequels from, no point in neglecting even the popular ones. In general new IPs are only created to replace the previous ones when they aren´t successful, just look at Sony, whenever they have a somewhat successful franchise they milk it and milk it and milk it, case in point Little Big Planet, Gran Tourismo, God of War and Uncharted just to name a few.

they are making new IP's but certainly not enough. their biggest most ambitious games are still Mario and Zelda. Sony has a huge amount of their studios work on new IPs for example, and of course, they recieve third party support which are making lots of new IPs like Destiny, Watch Dogs, The Evil Within and lots more.

Sony games sells less than Nintendo games. So it proves the "new ip" thing isn't the factor.

This year?
...they pulled off two new F2P games, both IPs established during this gen (Rusty's Real Deal Baseball; Steel Diver: Sub Wars) The latter actually fostered a large community for a time.
...they brought the Tomodachi IP to the west (It's so Japanese that it went mainstream for a time. Miiverse community is still huge.)
...they are to release Captain Toad: Treasure Tracker (Technically a new IP)

Three IPs. 2014.

or maybe they dont like to make those games. and there isnt much room for new casual IPs. there was singstar(and co), cod, wiifit, its hard to come up with new things like that.

i know you want to go into a "Sony vs Nintendo exclusives sales battle" but that has little to do with the point. to get new audiences that you dont have you need to create new content. chances are if somebody didnt play the last 10 mario games, he wont play the next one. fresh new software helps attract new consumers, its not a hard concept to understand. 

What baseless assumptions have I made?

Nintendo have made two new IP's for Wii U in two years. Nintendoland has done okay, W101 bombed. That isn't going to attract many new customers to their console. Therefore, for such a strategy to work, existing franchises have to be increasing in popularity for Nintendo to retain or increase their userbase. They aren't (apart from Fire Emblem!).

So what it comes down to is that there is absolutely no way Nintendo can be successful without creating new IP's. So why are they creating so few? Are they incapable?

I agree the Nintendo hardcore fanbase is definitely to blame. You only need to look at the hate so many Wii games get that dared to be anything other than Mario or Metroid. But they sold great because the silent majority was interested in those kind of games. Nintendo shouldn't be making business decisions to satisfy the hardcore. Their needs are too niche to base business decisions on.

Nintendo's reluctance to build new IP's is killing their brand

You have to first prove that they are reluctant to do so.

Secondly, you killed your statement my stating they have made and launched new IP's.

Third, Nintendo has a couple brands, including their own company name, which brand are they killing?

Fourth, you have to provide proof that new IPs is what is needed to revive their brand because old IP's are killing their brand.  

Nintendo does not have unlimited ressources. If they don't do Mario, Zelda and Smash  Bros, their sales would be even worse. The Wii U would be dead.