Most of the world...never was Christian. Christian --concepts-- have made life a whole, whole lot better...or did, for a time...in many Western countries, but most --individuals-- were not, and are not, Christian. Most people, both in the past and now, stay on the broad road.
There's some big differences in the way the world views life, human nature, etc. that make it harder for The Good News to take hold with many (post)modern, 21st century people. I read somewhere...this dude in the mid-60s said that modern man isn't looking for salvation; he's looking for understanding and therapy. Something like that. So...The Good News isn't therapeutic; its a condemnation of human nature and the world, with the only hope for anybody being...Jesus. That worked in the ancient world...they had mystery cults and such, the pagans had developed a sense of sin, or at least mankind falling short and needing correction, to be saved...but today...people would rather go "into treatment" or consult self-help or...you get the picture. We live in an increasingly "therapeutic" world where people have diagnoses, not sins, and need treatment, not forgiveness. Problem there is...well, speaking as a "mental patient..." a lot of times, they promise freedom but it leads to bondage. Even people who don't go for straight up psychobabble still think...and I think this is the spiritual component on 21st century mainstream thought...that the answers "lie within" or something. Kundalini yoga, drum circles, various gnostic and semi-occult takes on the spirit realm and such...that's being "spiritual, not religious," I think.
So...looking for "truth" ? Maybe. Looking for something...definitely. Some churches now mix components of The Good News with other things, ranging from legalism to easy believe-ism and an over-emphasis on grace. Many churches have "Biblical" 12 step programs available, counselors on staff, etc. The world's way of thinking has always had an impact on the church, and now I think a lot of churches are a little too influenced by the world's wisdom.
Its strange. Modern culture...is not very live-able, a lot of times. Wars, economic slumps and recessions and bubbles...wages in the US have fallen flat for many, very few peoples' wages have kept up with increases in worker productivity. The safety net has been largely shredded, while the TV encourages us to Keep up with the kardashians. Environmental problems seem to be getting worse...
...and those of us who turn to The Good News have --never-- been all that popular with the world, but I think there's growing hostility now. Turn to Deepak Chopra, you're "cool" and "spiritual"; turn to Christ, you're "hiding behind religion," etc.
I read that people are more concerned with being healthy and well-adjusted than with Truth. I think they're on to something. "Healty relationships," as defined by "experts" (of course...). "Healthy" ways to handle sex, food, the body, etc. That's very different from the Right way to live and the Right way to handle sex, food, the body, etc. Again, its a therapeutic outlook, not a moral one.
So...I guess we're all looking for something, but most people aren't all that interested in The Good News, at least not all of it, the whole Christian Worldview. Why some "get it" and dive in and others modify it and other reject it is...beyond my comprehension. I'm tempted to turn to Calvinism, lol.
Good question, btw.