Why are people whiny/negative on the Internet?
It's the internet. And they're people.
Why the strong feelings for the game?
Well, each person above has given their specific and personal take. I, like Tetsuro got into this game young and worked on it. To be specific, I started the year after it came out, picked up the RPG immediately, and have played both with fervor ever since.
In 2002-3ish, at merely 20-21, I was able to work on the 2d Edition RPG with Rich Wulf and Shawn Carman et al.
Later, I was able to do more work on a great number of the 4th Edition RPG books under Shawn and Rob Hobart alongside other beautiful Story Team members like Robert "Spooky" Denton, Maxime Lemaire, Mari Anne Murdock, and Fred Wan.
I got onto the Story Team the year, the very year, before it died. It was a dream that the 13 year old version of myself would have lost all bodily control of himself just thinking about. I got to affect the game behind the scenes and then...poof. Just like that. Gone.
But honestly, all that aside, this game has generated some of the greatest fans across ANY game. Players have given me cards for free to start me off. They've schooled me, taught me, bought me beers, and become deep, ever-lasting friends that let you crash on the floor of their house (looking at you Sparks). The fanbase of this game has been driven in part by the "win a tournament and you get to affect the story" aspect that drew so many into L5R from the word go. You only have to look at the ridiculous bounties (Ex: Martino's $1000 bounty at the last GenCon) to know how deeply they care.
This game, its people, and everything about it, is beautiful.
I hope Fantasy Flight is able to continue that, but I'm not worried because it will not all be on them. Many shoulders will be available.