This spring, I was introduced to a new specialist—Dr. Housing Bubble (www.doctorhousingbubble.com). In a recent blog, the 'Doctor' went to work diagnosing why new-home sales in many U.S. markets are still slumping.

In reviewing hard data like Census figures, Dr. Housing Bubble learned that despite slowly brightening employment, wage and home buying trends, many Americans are still living month to month.  

The 'Doctor' believes current first-time homebuyer trends are a reflection of even tighter budgets for groups like millennials. Many of these younger prospects have no desire to buy a home, providing a big boost to rental markets while dealing a hit to new home building.  

And for those who qualify to buy, low down payments are reflecting stagnant wage growth and evidence that many millennials are still saddled with mountains of debt, Doctor Housing Bubble says.  

That puts many recent post-bubble buyers in tenuous situations with negative equity lurking one tiny recession away. And with so many American families on the razor’s edge of monthly payments, the blog concludes that any tiny deviation on interest rates can "price them out."

In some markets, the blog points out that affordable new homes are being developed to cater to first-time buyers. But, in more expensive metro areas where younger people are flocking—potential first-time homebuyers simply can't afford rents let alone the cost of a modest home.

Besides first-time homebuyers dropping to about 30 percent of all sales compared to 2009 and 2010 where it was around the 50 percent mark, they are generally coming in with low down payments. In fact, the 'Doctor' calculates that today, 66 percent of first-time homebuyers are entering the market with low down payment loans, versus 2009 when the number was 77 percent.

Doctor Housing Bubble believes that the bust that took place a few years back made prices more affordable for a short window before investors pushed prices higher. Now, those investors have crowded out regular buyers, while pushing first-time homebuyer figures lower.