It's an age-old cliche: science vs religion. Faith vs reason. As though the two are opposites; as though neither can live while the other survives (to quote Harry Potter tongue-in-cheek). As though they are locked at each other's throats in an eternal battle to the death. One will vanquish the other eventually, and for now the victor seems to be science. I mean, it's obvious, right? Religion is fast becoming irrelevant in the developing world for several different reasons.
First of all, no more fear of the unknown. People know why things happen now, without having to use God as an excuse. God is now considered to be a 'safety net'; a vain attempt to ward off the threat of looming death into something more friendly. Self-delusion, wasted hope, whatever you want to call it: in their opinion, that's religion. They want to see themselves as people who can depend on themselves, not on some foreign unseen deity in the sky.
Then there is the problem that people have with the whole 'organized religion' thing. Churchmen, sheikhs, rabbis; they are all seen as clinging to traditions of the past (whether the traditions are good or bad). Our century is all about shaking up institutions and religion is being treated no differently.
Finally, most people aren't choosing their religion anyway. They take the convenient way out - following their parents' beliefs, mostly without any real conviction. Religious holidays have become empty rituals to be followed half-heartedly, for example; church every Sunday, or the mosque every Friday - even Islam's five daily prayers - has become a drag. Because who's going to go for something they haven't been motivated for, haven't chosen, in the first place?