Millennials who are able to be homebuyer prospects are seeking not only smaller houses, but also ones that are more energy efficient and healthy.
They are moving out of cities, which are too costly and seeking houses that are smaller and require less maintenance and lower expenses for heating and cooling. The houses are less expensive to purchase and operate and offer the opportunity to enjoy more leisure activities.
Both Millennial partners most likely have to work in order to afford being a homeowner. Therefore they have less leisure time. What extra time they do have, they prefer using it to enjoy outdoor activities such as hiking and biking or traveling, rather than spending their time performing household duties like mowing lawns and cleaning gutters.