Someone who was struggling mightily to stay involved in the LDS Church once asked me why I remain an active, "believing" member. The following is my response - a short, bullet-point summary that doesn't do full justice to the question but hits some highlights:
I am LDS:
because I absolutely love the theology and "cosmology";
because it's the truest thing for me I've found - and it's not close;
because I don't really care all that much about what people think of me;
because I've carved out a place from which my heterodoxy doesn't matter and isn't a threat at all to the Church and the rest of the membership;
because I really love the people in my ward (even those with whom I tend to disagree quite strongly);
because my wife and kids also absolutely love the Church;
because plenty of other people outside the Church envy the peace and happiness I've found in "my faith" and have been helped in real and lasting ways by it;
because I don't want to make a major change to something else with which I will agree less (especially at the "pure" theoretical level);
because I've learned to let most of the cultural crap with which I don't agree roll off my back;
because I can talk about those things with which I disagree that people say at church with my wife and kids without them being threatened by my disagreement, even when they don't agree with me;
because I have a deep and abiding "testimony" of what I perceive to be the core principles of the Restored Gospel of Jesus Christ;
because I'm Mormon at heart.
I am LDS largely because it's part of who I am (because my own "I AM" is LDS) - and because of some very intense, very personal, very powerful experiences that also simply are part of ME.