The housing market is about to have its slowest year since the real estate bubble burst in 2008, according to National Association of Realtors

At its current pace, total existing-home sales in 2023 are projected to amount to 4.1 million, according to NAR. That would be the lowest number since the subprime mortgage crisis of 2008—a year that also saw the unemployment rate spike to nearly 8% and millions of Americans’ home equity evaporate. By comparison, there were more than 6 million home sales in 2021, NAR data shows.

High mortgage rates and rising home prices are largely to blame for the shrinking number. The U.S. housing market has gotten so expensive, in fact, that Andy Walden, vice president of enterprise research for ICE Mortgage Technology, calculated that U.S. incomes would have to increase a whopping—and highly unlikely—55% for it to be considered affordable. 

“Those are massive movements that we’re talking about,” he recently told Kelly Evans of CNBC’s The Exchange. “None of them are going to happen in a vacuum. None of those one single factors is going to make the move.”

While 2023 will likely mark the slowest year since the infamous housing crash, home sales have been slowing since last year. 

“Time flies, but it was this time last year when we really started to see the market slow down,” Erin Sykes, chief economist at residential real estate brokerage firm Nest Seekers International, tells Fortune. Sykes said she started noticing the shrinking transaction volume in 2022, but it took more than six months for national data to reflect the slowdown, she adds. 

What’s really discouraged buyers from buying and sellers from selling is the continued rise in mortgage rates. The average mortgage rate has more than doubled since the start of last year, adding hundreds of dollars to the monthly cost of a home and slowing the number of sales. 

“Today’s housing market is the slowest since 2008 because of limited quality inventory and rising interest rates, which price out potential buyers,” Armstead Jones, a strategic real estate advisor at Real Estate Bees, tells Fortune. “The gap between what buyers can afford and what sellers are asking is a wide margin. That difference leaves longer days on market and little to no sales activity.”

The “lock-in effect” can also explain the slowing of existing-home sales. Normally, existing homeowners looking to move or trade up are responsible for a large portion of homes on the market. Current homeowners who bought when rates were below 3% during the pandemic are reluctant to reenter the market as mortgage rates are climbing toward 8%. Indeed, more than 90% of existing homeowners are locked into mortgage rates below 6%, Odeta Kushi, deputy chief economist at Fortune 500 financial services company First American, tells Fortune. 

“These homeowners do not have a financial incentive to sell,” Kushi explains. “The combination of reduced affordability and an even stronger rate lock-in effect suppresses home sales because you can’t buy what’s not for sale, even if you can afford it.”

Plus, prospective homebuyers are taking a “wait-and-see” approach, hoping that mortgage rates will fall soon. However, many economists and real estate experts project that mortgage rates likely aren’t going anywhere for at least the next year. 

“Longer-term, higher mortgage rates are likely to be a drag on home sales as costs put buying out of reach, causing many households to delay plans to move,” Realtor.com chief economist Danielle Hale previously told Fortune. “The bigger the gap between market mortgage rates and the rates homeowners enjoy on their existing mortgages, the more likely it is that homeowners are to feel locked in place and choose to stay put.”