A version of this article first appeared in CNBC’s Inside Wealth newsletter with Robert Frank, a weekly guide for high-net-worth investors and consumers. Sign up to receive future issues directly to your inbox.

Auction sales during Monterey Car Week fell 3% from last year as a shift from older to newer cars led to a buildup of unsold classics from the 1950s and 1960s.

According to Hagerty, the classic car insurance company, total sales at this year’s five Monterey auto auction houses – RM Sotheby’s, Broad Arrow, Gooding & Company, Mecum and Bonhams – fell from $403 million in 2023 to $391.6 million this year. This followed a 14% decline last year compared to the peak in 2022.

Of the 1,143 cars listed for sale, only 821 were sold, a 72% sell-through rate according to Hagerty. The average selling price was $476,965, slightly below last year’s average of $477,866.

Experts say wealthy collectors still have plenty of money to spend and are confident about the recent rise in stock prices, but the type of cars they want is changing. There have simply been too many similar cars at too many auctions to attract high prices and sales.

“There is a saturation,” says Simon Kidston, founder of Kidston and leading adviser to high net worth car collectors. “Walking through the auctions and seeing so many similar ‘products’, I wondered if any of them had thought about what they or their competitors had already put on consignment and if the cars were vying for the same buyers. Add to that the fact that many listings have been sitting in dealers’ windows for months or years, which always feels like shoddy B-stock.”

At the same time, a new generation of collectors is driving the market – mainly Gen Xers and Millennials – and prefers cars from the 1980s, 1990s and 2000s. The classic cars from the 1950s and 1960s that drove the market for decades and are popular with the baby boomer generation are flooding into the market and finding no buyers.

The sell-through rate at Monterey (or the percentage of cars that actually sold on the auction block) was a paltry 52% for pre-1981 cars selling for $1 million or more, Hagerty said. The sell-through rate for cars younger than 4 years old was a much higher 73% — proof that young collectors are now in the driver’s seat.

Hagerty’s Supercar Index for sports cars from the 1980s to the 2000s has risen over 60% since 2019, while the Blue Chip Index for Corvettes, Ferraris, Jaguars and other legendary classics from the 1950s and 1960s has fallen 3%.

Admittedly, a small number of rare, true masterpieces will still fetch high prices. The top car of the week was a 1960 Ferrari 250 GT SWB California Spider, which sold for $17 million at RM Sotheby’s. In second place was a 1938 Alfa Romeo 8C 2900B Lungo Spider, of which only five examples exist.

But the general changes in the classic car sector – especially as many older collectors begin to sell or downsize their collections – will likely continue to weigh on prices for older cars for years to come.

“From an auction perspective, the market continues to hold its breath as we move from what was hot, like Enzo-era Ferraris, the so-called full classics and sports racing cars of the ’50s and ’60s, to the emerging class of modern supercars,” said McKeel Hagerty, CEO of Hagerty. “The divergence between older and newer cars has accelerated.”

Some believe that high interest rates are also putting pressure on the classic car market. At the lower end of the market, many buyers had used financing to buy cars and build their collections. At the higher end, rising interest rates increased the opportunity cost of buying a classic car.

“People think, ‘Instead of this million-dollar car, I could make 5% or 10%,’ if you have a good manager,” Kidston said. “That makes people think more than anything else. A collector car is partly an investment. There is no other reason for the increase in value of collector cars over the last 40 years other than the investment aspect.”