Because of the "poor diagnostic test" formed by systemic coercive factors, a few of which were discussed here previously, which keep non-believers in the church despite lack of true belief or desire for true belief, there are lots of people in the pews who really have no business being there. As described by Jesus in Matthew 7, it's quite possible that many of those calling "Lord, Lord" today are not in fact true believers, so it stands to reason that with lower barriers to exiting, more people will leave the church. With relatively recent technological and social changes, many of the barriers to exiting religion discussed previously are losing their effectiveness. A life outside the church is more of an option than it has ever been, and it continues to be more and more viable every day.
So Christianity in American has a decision. It can try to appeal to the non-believers in the pews with bells and whistles like coffee shops, modern music and an easy message of heaven and prosperity, trying to hold onto as many of its "flock" as it can. Or it can focus on building a strong core of true believers by strengthening its message of love and self-sacrifice. With a presumably-continuing loss of the previously-discussed barriers to leaving the church, the former option would lead to a long but inevitable decline. Instead of numerous powerful competitive advantages, a church trying to continually reshape itself to appeal to a modern audience's sensibilities would face a distinctly sharp disadvantage, in the sense of competing with other forms of entertainment for non-believers, by having to include the Bible in its "shows".
That modern Christian music sucks is a clear and obvious fact. But the question is: why does it so clearly suck? It has to do with Christian musicians being hobbled by having to stick to a particular message. While other bands can sing about sex or world peace or food, Christian bands have to focus on one particular thing every song on every album. Similarly, Christian church services make for bad entertainment for a non-believing audience. Joel Osteen's massive self-help sessions are hobbled by the necessity of including that darn book.
All the bells and whistles of a typical church service are necessary to keep non-believing butts in the seats. For people who are there out of pure habit, or to keep their mother happy, or for any reason other than belief or seeking belief in the religion, the accoutrements of a church service make the obligation of an hour a week a bit more palatable. A weak, milquetoast message of easy Christianity can also make it easier to sit in church bored, but it's not going to keep people coming back as the barriers to leaving get lower and lower.
As exiting religions becomes easier, the church can no longer hope to hold onto its apathetic, non-believing elements. Rather than futilely weakening its message and losing some true believers in the process, the church would be better off to focus on the actual themes of the Bible, which makes it clear that it's hard to be a Christian. The average non-believer in the pews doesn't want to hear that. Preachers and bishops who depend on those non-believers putting money in the collection plate to pay for their salaries and pensions might not be particularly motivated to tell them that.
The last time in Western history it wasn't easier to go to church than to not was before Emperor Constantine's conversion 1700 years ago. Up to that point, you had to really want to be a Christian to do it., and church members were fiercely devoted to biblical principles of charity and non-violence. Once religion became the default option in society, the church was weakened by the presence of non-believers who wouldn't countenance such self-sacrifice. As the dominance of the church gradually recedes, these non-believing elements will leave one way or the other. It's up to the church to decide if it will wither away while weakening itself in a vain attempt to hold onto them, or it can return to pre-Constantinian principles, inviting anyone who doesn't truly agree with biblical teaching to leave but also developing and holding onto true believers. Biblical teachings can either be a disadvantage in a doomed effort to hold onto non-believers or an advantage in developing a strong Christian community.