I have encountered five basic motivations among educated people (which I'll also interpret as smart/thoughtful, but disinclined to think too hard; best-case scenario), along with my estimated percentages:

1. Pain Aversives (40%): This is a challenging subject to think about emotionally speaking. It involves forming an opinion about such unpleasant subjects as evil and death. For some people with a very low threshold for intellectual pain, the first bit of hurt is enough to make them draw back, adopt the nearest reassuring belief, and never poke too much ever again. These people are distinct from the socially religious types, who haven't thought about the subject even enough to develop a pain-based aversion reaction. They genuinely believe, but at a carefully superficial level. If the thoughts come back to haunt them, they quickly call up a friend and go watch a movie.
2. Belonging (30%): To feel part of something bigger than themselves, anchored by a sublimated need for a parental force in their lives (sublimation is one of the major defense mechanisms), and a sense of order and there being a "plan." These are typically sociable, extroverted doers/execution types.
3. Optimism (15%): Surprisingly, this is a common one. Atheism is a somewhere between neutral and pessimistic out of the box. It takes some intellectual contortions to make it an optimistic belief. Religion, on the other hand, is optimistic out of the box. For some people the process really IS that simple. They look at the belief systems available, and choose religion over atheism because it is "less depressing."
4. Intellectual Intimidation (10%): This is a fascinating type. They often have PhDs in religious studies and have a very scholastic approach to their belief. In this category I put all those with a collection of conditions holding a) very little training in very precise thinking (like math, logic, programming, analytical philosophy arguments etc.), b) a dominantly associative and aesthetic style of thinking c) too MUCH training in very ambiguous thinking behaviors, like po-mo essay (writing using words/phrases like "decentered" or "dead white male" or "always/already"), stream-of-consciousness fiction etc. and d) exposure to modern theological material that deals a lot in symbolism, vaguely Freudian psychology, textual analysis of religious sources, very detailed historicist analysis etc. A clear sign is when people spend time reading fat books with titles like "Reading the Resurrection: Aquinas vs. Kierkegaard." When these factors combine, people can get so caught up in the intricate world of pseudo-sophisticated religious discourse with lots of vague philosophical terms, quotations from somewhat refined theologians etc., that they can lose sight of the fact that the foundations are deeply, deeply silly. This is the mental equivalent of walking into St. Peter's Cathedral and being so impressed by the architecture, you decide the religion must be true. All big religions build both physical and intellectual cathedrals to intimidate people with sheer size, scale, technical refinement (of craftsmanship in one case, arguments in the other). In a way you can think of religion as what you choose to put in the empty metaphysical space left over once you eliminate the stuff that science takes care of. Some people simply fill it with intricate, heavily-footnoted/end-noted/citation-loaded crap until there is no room left to actually think.
5. Mystical experiences (5%): People who undergo "mystical" experiences (these exist), but lack the scientific knowledge and metaphysical sophistication required to make sense of them resort to religious understandings of such experiences. This is exacerbated by the fact that the "content" of such experiences is usually shaped by the most familiar frame of reference you have available for metaphysical thoughts, not the one you believe in. So even if you are an atheist, but there's simply a lot more data about (say) Christianity in your head, chances are, your mystical experience will have Christian elements to it. Pretty much any earnest belief system works to fuel mystical experiences (farcical ones don't; I have never heard of or read of a mystical experience framed in terms of pink bunnies or flying spaghetti monsters... probably because farcical belief systems lack sufficient narrative density to serve as fuel).