Eve ebbs and flows much like real life. There are peaks and valleys, active times and not-so active times. Many factors encroach and effect these times, real life, in-game changes, personal issues, enthusiasm for the game itself... any number of factors can factor into the factor... we all know this.
I've found that big valleys come in my play schedule after big moves. Jumping ships and mods into a new area over the course of a week or so seems to tap me out. Mostly it drains my enthusiasm for the game. Anything that tends to make "playing" Eve more like work does this to me. When Eve starts to feel like "work" it saps some of the fun from it, making it less and less desirable. Especially when the rest of your life is demanding of your time, you're especially busy or other things you want to spend time doing are available.
This isn't revelatory, only worthy of discussion. It comes and goes. Things change. This is natural. Over the course of nearly two years of playing Eve I've learned to expect them. Early on I thought these valleys meant the end of playing Eve, I thought about stopping many times early on. Of course, back then, you had the problems compounded by being a Noob and sucking hard. That didn't help. But I stuck with it and those particular issues are behind me. Somewhat, heck Eve is a harsh mistress that never lets you believe you've "made it". No matter how many skill points you rack up.
I'm in a valley right now. It won't last. But valleys are useful as well. I can't operate on the peak all the time, you need to catch your breath and look around. Where am I? Where am I going? Am I doing the right thing for my characters, am I on track, do I even have goals? These are all questions I'm asking myself right now.
To be honest, some of the answers are not what I expected them to be.