I'm pretty damn sure Nintendo "tried" to fill in the gap Rare once occupied. But let's see, Nintendo goes from having one "productive" external multi-team super dev. house in Rare, to basically nothing, with the exception of the 1Team/1Game hatchlings Retro/NST/SiliconKnights. (getting lots of money was nice, but it doesn't make mid-stage game projects overnight). So yeah, Nintendo only had 3rd party devs/pubs to turn to to get games made (dunno if they were tired of their 2nd-party strategy at this time).
Who said it was going to be easy (for Nintendo)?
As I see it, Nintendo basically spent the past few years "buying drinks" for all these 3rd parties, trying to approach them as partners rather than competitors. Probably a difficult thing when: they ARE competitors, and their console isn't a runnaway success/#1. I believe they have been moderately successful, and I think I've gotten a healthy handful of significant games from those deals. I've personally gotten more games and more VALUE out of these 3rd parties than what Rare offered me on N64 -- and I seriously doubt most of these games would've come our way if Nintendo just sat back and let the 3rd parties be the "financially and creatively sound" entities they are.
It's apparent that Nintendo and the GameCube simply didn't have a lot to offer to those 3rd parties at the time. So productivity was slow and thin at best, but it seems to have built a better collaborative platform for hopping onto Rev (and DS), which stills looks more promising than the the jump from the N64 to the GameCube.
Pre-GameCube, I was excited about your standard potential Nintendo/Rare franchises everyone else was excited about, plus Rogue Leader.
Pre-Revolution, I'm not mainly excited about the familiar Ninty franchises we "can't live without." I'm excited about Suda51's game, I'm excited about the funky unknown new Nintendo property, I'm excited about whoever is willing to dare.