There are lots of homeowners who are reluctant to sell their houses because they don't want to lose the historically low mortgage rate they have on their current home. (Data shows 51% of homeowners have a mortgage rate under 4% as of April this year.)

For those who have decided to sell, the primary reason is the realization that, after so much time spent at home, they wanted different features and amenities in their home. Other factors are they realized that their current home could no longer meet their needs. Additionally, remote work and whether or not they need a home office or are tied to a specific physical office location also factored in, as did the desire to live closer to loved ones.
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Even with today's mortgage rates, overall lifestyle needs are a significant motivating factor for many sellers.
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Source: The 2022 Summer Sellers Survey by realtor.com