I don't know why I'm still interested, but I am. I started back on June 11, 2013, and haven't missed a day yet. I've had quite a few dropout over those near 20 months too, but I still play this thing everyday. I know some I played with burned themselves out speeding through the game. They said they "may comeback" to playing again, but I'm starting to doubt they will, they will probably comeback when the next one comes out. I saw the same thing happen in 2007 with Wild World, people stopped, but came back in 2008 with City Folk.
I think what keeps me coming back is that I set yearly goals. My first year was to get all gold badges, something I was able to do! StreetPass was the final one, and took having 4 freaking systems to get enough tags in time. The next goal is what I'm in now, and it's to grow/arrange my flowers, including all hybrids- as well as keeping all 10 villagers (so far, 15 months later all 10 are still there). So far, this flower growing is one of the slowest things I have ever run across in a video game! It still excites me though when I start up the new day with the anticipation- did I get any new hybrids? I already set year 3 goals, and they're not really all that challenging- reach 1,000 continuous days (shouldn't be a problem given I'm over 600 now, and this is on a handheld system, not like I HAVE to be home to play it), reach 1,000 visitors (approaching 700 now), obtain 12,345 island medals (easier than you think, I crossed 11,000 already), and "goldify" one of my player houses- setting up furniture now to prepare for the challenge, then I'll return his house interior back, and give away the furniture. After that, I don't know, year 4 may be when I'm "done" with New Leaf- as if I'll ever truly be done, I still play Wild World periodically approaching 10 years after I got it!
Oh, almost forgot. February, 2014 I picked up the Japanese version of New Leaf, and also play that town everyday, and I take my NA one to get some Japan only events to get items. Setsubun will be the last holiday I haven't experienced yet in NA or JP, so that will keep me interested through at least next month. Hopefully, all my flowers are grown, so I can start helping my Japanese player get a better looking town by taking my American player over there with some extra hybrids he was able to grow the next few months (I have the Beautiful Ordinance in NA, Night Owl in Japan, so I can't do too many, Japanese one will have to water all these).