It’s always been a sort of final chapter of the American dream: Get married and have kids. Buy a house. Move to a bigger house. Downsize to a smaller one.

But a growing number of aging baby boomers are saying, “No, thanks” to downsizing, choosing instead to remain in the same sprawling houses in which they raised kids and created lifelong memories.

“We’re just not seeing that much downsizing,” says Alexandra Lee, a housing data analyst at Trulia, a real estate research firm.

While many older Americans are still stepping down to smaller homes, they’re doing so later in life. The trend is contributing to a housing supply shortage across much of the country.

There are other factors as well. Boomers, generally those age 54 to 73, are working longer and putting off retirement. Many of their millennial children are living with them well into adulthood. And there’s a dire shortage of less expensive entry-level houses across the country, pushing up prices in that category and making the trade-off less appealing.

Fifty-two percent of boomers say they’ll never move from their current home, according to a Chase bank survey of 753 boomer homeowners released earlier this year. Chase doesn’t have comparable data from an earlier period. An Ipsos/USA TODAY poll of 45- to 65-year-olds in 2017 found 43% anticipated remaining in their current residence through their retirement, possibly indicating the share of non-downsizers is rising.

Many boomers are staying in their longtime homes and communities because they’re deferring retirement. About 20% of Americans 65 and older are working or looking for jobs, up from 12.1% in 1996, Labor Department figures show. Older people are staying in the workforce because they’re healthier and will need bigger nest eggs to finance longer retirements, according to Jennifer Schramm, senior strategic policy adviser for the AARP Public policy Institute. Also, many older workers’ retirement savings were hammered a decade ago, she says.