Nintendo isn't obligated to do shit. If they wanted to they could cancel Zelda U & put the series on an indefinite hiatus and there would be nothing u or anyone else could do about it.
Guess what? 2D Mario is a far more popular franchise than Zelda and neither N64 nor GameCube received an exclusive entry, they didn't even receive ports/remasters, the series took an 18 year hiatus on consoles. Metroid skipped N64 and had 8 years between Super & Prime. Kid I cards was dormant for 21 years. Pikmin went 9 years between 2 & 3. Luigi's Mansion went 12 years without a sequel. Pilotwings went 15 Yeats between releases. Star Fox Zero is the first in 10 years. Punch-Out went 15 years. F-Zero hasn't gotten a new release in over a decade. The list goes on.
Nintendo can do whatever they want and a few people bitching on the Internet aren't going to stop them from doing what they think is best for their business.
And its these exact business decisions and lack of caring for what the fans wanted that got them where they are now. It's time to stop pissing their fans off wouldn't you say?
Nintendo fans aren't a single collective sum of people who all want the same thing. The people who complain on the Internet are a very small minority.
Based on the vocal forum goers, u would think Metroid was one of the most popular series ever but it's super fucking niche. The series averages 1-2 million per game, that's worse than Mario Party, a series that is often hated on.
Games like Tomodachi Life and Happy Home Designer were talked about on forums as if they were going to bomb yet they are multimillion selling games, games like Bayonetta 2 & Xenoblade X were talked as game of the year material yet both are very niche.
This kinda shows that the vocal forum goers are not the typical Nintendo audience.