"Spiritual but not religious". As an underlying philosophy, this has never been more popular, alongside a vocal disdain for "organized" religion. As I discussed numerous times now, this reflects the popularity of Gnosticism in American society, and Gnostic energy often gets channeled in a Buddhism direction, owing to key parallels.
Let me just review Gnosticism (see here and here for earlier discussions). Traditional Gnosticism believes in a Platonic metaphysical dualism that sees the world and all of creation as evil. Since creation is evil, it cannot have been created by a benevolent God. No, the creator is an evil God, a demiurge, often identified with the God of the Jews. Beyond all this lies a greater God, a good God. And here is the crux: within every human being lies a "spark of the divine" that is itching to be re-united with this greater God and escape the confines of the evil materialistic world. And how to escape? Escape comes through knowledge, gnosis, often hidden esoteric knowledge available only to a select few.
Now, at least on a superficial level, this has some overlaps with Buddhism. At is basis lies the underlying principle that life involves and endless cycle of suffering, and suffering is rooted in desire. The Buddha, Siddhartha Gautama, provided a basic road map to escape the cycle through the suppression of desire. The term "buddha" is used to denote anybody who has attained "awakening" (enlightenment/ Nirvana) and has escaped earthy suffering. Many are taught this knowledge by others in an esoteric fashion.
Many like to argue that the advantage of Buddhism is that it has no doctrine, is not organized, and it has no notion of a personal God. It is easier, conceptually, to view it through the frame of Gnosticism. Buddhism and Gnosticism both see the difference between "God" and creation as one of degree, not of kind, and view humanity as returning to some kind of equality with "God". Creation is not good, and the ultimate goal is liberation from the world. Of course, such an escape is not simple, and requires arcane knowledge ("gnosis") and ardent practice, and is only available to an elite few.
In contrast, Christianity views creation as the result of a beneficial Creator. God created everything that exists from nothing. Creation is good, but humanity is sinful. The essence of Christianity then, is that God became human to overcome this sin, and to allow humanity to become one with God. Note the clear difference: union with God is not a natural "homecoming"; it is rather a gift, a privilege. Moreover, this form of salvation is available to all, not just a small elite. The "institutional" church is simply the entity through which Christ mediates grace.
Why, then, are so many Americans attracted to Buddhism? Actually, what they seek is Gnosticism, rather than Buddhism. They merely see much of Gnosticism inside Buddhism. Part of the attraction springs from a very post-Enlightenment denial of objective truth. If truth is more relative than objective, then how can there be such a thing as sin? It's far easier to assume a natural unification with God after death, with no heed for the consequences of your behavior. Who needs doctrine when all that matters is the "spark of the divine" within me? Experience trumps everything! At the same time, the entrenched individualism in American society rebels against anything vaguely communitarian, especially an entity that claims to know the truth. Far easier to follow your own path! This can so easily feed the narcissism and sense of entitlement that pervades much of modern American culture and society (is it any wonder that Buddhism and Scientology are most popular in Hollywood, the ultimate pit of narcissism?). The notion that one can be a sinner is repellent in the popular mind. No, Gnosticism makes you feel special. I'm OK, you're OK! Do what makes you feel good!
There is a darker side to this, of course, as it can feed into the doctrine of American exceptionalism, that sees America as unique, specially blessed by God, not subject to the same rules and constraints as other countries. And if creation is not fundamentally good and in need of renewal, then why should be it not exploited through violence and environmental degradation?
This lies at the root of the American love-affair with Buddhism, and why it is seen as superior, better than those nasty "organized" religions. Though I would contend that Buddhism has some serious flaws, much of this crowd is attracted to a very shallow version of it, a Buddhism of the mind, not rooted in reality. Note, for example, that traditional Buddhism is concerned with suppressing the ego, the very opposite of the modern American instinct. No, Gnosticism is at fault, and Buddhism is largely guilty by association.
One final thought: one of the much-touted "attractions" of Buddhism is that it is inherently peaceful, tolerant, and non-violent. This is utterly false. Just look to the political turmoil in Sri Lanka. Here, a nationalistic and xenophobic brand of Buddhism is highly influential among the Sinhalese minority, and is not above denying equality to the minority Tamils, or using violence to impose its will. Remember too, in Vietnam, it was the Buddhist monks who burned themselves to death. And yet the Hollywood brigade tends to ignore these inconvenient facts...