SAN DIEGO (KGTV) -- A new report is looking into why there is a shortage of homes for sale around the country.

According to the report by NerdWallet, in October of 2017, the US had a 3.9-month supply of existing homes for resale, meaning at that pace, it would have taken 3.9 months to sell all the homes on the market.

According to NerdWallet, a supply under six months places home buyers at a disadvantage.

The report identifies six reasons why the housing supply is so low.

1. Boomers aren’t moving

Over three-fourths of baby boomers own their own homes, according to the report, meaning millennials don’t have enough homes available to buy. The report also found that rising home prices force baby boomers to stay put because they don’t have the cash to downsize.

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2. Landlords won’t sell

NerdWallet says millions of single-family homes were converted to rentals after the foreclosure crisis. In 2017, renters made up 36 percent of households. A greater demand for homes coupled with less supply means values rise while rents are rising faster than home prices.

3. Low mortgage rates

The report points out that interest rates on outstanding mortgages averaged about 3.8 percent over the last three years. As mortgage rates rise, fewer people are interested in selling and getting into new mortgages.

4. Entry-level homes ignored by builders

In the first nine months of 2017, nearly 500,000 newly-built homes were sold of which 55 percent sold for $300,000 or more.

NerdWallet says builders blame high land cost and a lack of skilled construction workers for not building more entry-level homes.

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5. Regulations add cost

The report points out the homebuilders say environmental protection, infrastructure fees and rules that specify lot sizes all add tens of thousands of dollars to the cost of building every single home.

According to the report, regulations account for roughly one-quarter of the cost of each home.

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6. Owners want a restricted supply

Finally, the report found that local zoning and land-use regulations are enacted by officials elected by the people. The report says those officials are only responding to constituents who want a limit on the number of homes that can be built in a neighborhood. Elected officials can also set a minimum square footage for homes, further limiting supply.

“There are regulations that are more about the neighbors’ sensibilities than they are about the safety of the people living in the houses,” says Miriam Axel-Lute, associate director of the National Housing Institute.

“It’s neighbors who want their property values to go up, in most cases, who are insistent upon some excess safety design standards or minimum lot sizes or other things,” Lute says. “They either want their property values to go up or they don’t want, quote, ‘the wrong sort of people’ in their neighborhoods. This is the pressure behind a lot of the most damaging regulations out there.”