There are many reasons that I can think of why people are having trouble getting married, or perhaps I should say do not seem to want to get married.
First, there is the problem of assimilation.
It is now the way of the "western world" to view marriage as a burden, a set of shackles, the end of the road. Something to be entered into with reluctance, and deferred as far as possible. Just watch "Married with Children" (a TV show) and you will see what I mean. Than there is the divorce rate that is well over 50%, and most of media talking about failure of the marriage institution. (nobody says "why do smart people fall in love")
As people who received Torah at Sinai, we should know better than to fall for such attitudes, but what can we do, foreign attitudes have crept into many frum looking homes in America, not to mention the recent ba'al teshuba universe where these influences are understandably stronger.
Second, there is a problem of trust.
Even though everybody knows that it is Hashem who makes the matches between people, not everybody actually believes it in their heart. Why? In my opinion, it is a sense of disappointment. They look at a large number of marriages that are so far from perfect, and wonder what could Hashem possibly have to do with such a mess? If they took trouble to understand the process, and find out exactly how does the matchmaking happen in the heaven, how are the souls paired, what is the point of the pairing, etc. they would see the astonishing precision and beauty of Hashem's work. There is no lack of printed or online materials on the subject. Numerous authors give wonderful overviews of the subject, with references to Gemara, Scriptures, etc. But this material has to be read to be of any use
Third, the problem is that too many people are jaded
After a number of unsuccessful attempts, people tend to get discouraged. They don't believe anything anymore, and tend to develop a jaded outlook. With this attitude, they could easily meet their sole mate and ignore, repel or reject them. The cure for this, in my opinion, is in being able to forget the past experiences. The ideal, I think, is to approach each date as if it is the first and the last one. If you read financial papers, you may notice that mutual fund advertisements will usually tout their superior returns over the years, and then they will have a line of fine print that says something like "past returns are not an indication of the future earnings" or something like that. I think the challenge is to stay innocent despite of everything, because there is value in being innocent (not to mention a mitzvah. See Bamidbar(Numbers) 18:13).
But the biggest problem, I think is in lack of education.
How many of us understand what marriage is all about. Why is it that Hashem said "it is not good for man to be alone" Gen. 2:18? Why is it that father of Moshe and Aharon, the great tzaddick who never committed a sin in his life, was reprimanded by his little daughter because he divorced his wife and by his example cause others to separate from their wives? Can we really blame him? He saw children being drowned in the river, and he gave up, that's it, enough, no more point in this – he said. But Miriam, who was already a prophetess and a young age, saw clearly that there was more to this than met the eye. And in fact, after he remarried, Amram fathered Moshe. Do we really understand what it means that Hashem's presence dwells in Jewish homes, do we know what it is like to be roommates with the Creator of the Universe? There are many questions that should be asked, and many answers that should be sought out. I think somewhere in that process of questioning and learning, we will get a sense of what is our mission, and why marriage is crucial to it. If, however, we fall into the "All American" non-inquisitive, couch-potato passivity, than we will reap ignorance and bitterness.
Good luck to all.