None of the console manufacturers launch in March, 3 months before E3 and 7-8 months before holiday season.
And?
They launch in November, and then have nothing for months after until E3 so you'd think they'd actually be the ones who should have announced far further into the future than what the Switch is doing. The Switch can focus on launch, start off with a launch + launch window momentum and then offer the "long term" proposition at E3 as most other publishers do (all the same) but in a shorter time frame, potentially allowing for a nicer momentum packaging up front.
And, again, you have zero appreciation of time management with what you're asking for, straight up. Nor do you seem to have any appreciation for how noisy a launch event is for news immediately thereafter, its going to be a total clusterfuck to announce anything of worth down the road unless it either gets buried or it buries something near launch. Go look at the news from the PS4 and X1 launch, its a right mess of hardware, OS, software (OS), and software (games), on top of other random sides and opinions and impressions.
The message at a reveal is about the launch and its software, and they need that to be clear both from themselves and in how the media covers it. They can't reveal 30+ games and then announce the Legend of Space Fire Emeblem staring Samus Aran, and have it dominate everything while also being year+ out.