(1) It’s has decided not to move it’s theology with the moral progression of the world – essentially being ‘left behind’ on moral grounds (which was it’s point of interest)
(2) Christianity is really hard to nail down. What are the beliefs exactly and what is essential to one’s faith in God? How is one’s faith supposed to look? With some 100+ denominations and varying beliefs between them as to importance of certain issues – it becomes confusing.
(3) It’s got quite the sordid past. For a religion centered around love it has a lot of skeletons in the closet that make one re-think this premise. Maybe the foundation is not love, but conformity and institutional adherence? It’s got a serious PR problem and makes no bones about its past.
(4) It’s in a Western society of individualization but demands a culture of confomity to their societial rules; many people cannot make a committment that relieves them of their own thinking.
(5) It’s definitions of certain areas is short-sighted. For example, worship comes to mean the service you attend and the musical aspect of that service (or praise). It’s fairly clear that worship is a much bigger idea but it is hard to determine if this is the case within some churches.
(6) Christianity does not speak for the current problems in society. It does not neccesarily address global warming, pollution, poverty, problems in capitalism, the food industry, etc. In this sense, it is deciding to stay neutral which is as good as being irrelevant.
(7) Christianity is thoroughly steeped in capitalism and politics and reduced itself to irrelevance in face of the new ‘religions’ and definers of daily ethics – business/work. With this faith being so steeped in the processes of capitalism, business, and gov’t – it does not realize the usurption happening.
There are probably more reasons – like dis-satisfaction – but usually we can find our faith being reduced by the religious restrictions we find in the institution. This in turn makes us ask the tougher questions like ‘how important is this place to my livelihood/living’? This is when we start to find out some stark realizations, ‘not very’.