You need to differentiate between liquid and illiquid assets, because they represent different kinds of wealth.
The person with a $1.8M property holds a very valuable illiquid asset. They cannot convert the value to cash trivially (they could perhaps take out a home equity credit or remortgage the house). Effectively none of the value of asset is available to them to meet any other needs, and will only be fully realized when the house (their home) is sold.
The person who can pay the mortgage on a $1.8M property has substantial income and/or cash reserves, which are liquid assets and thus distinctly different from the property owned by the previously discussed person. They may not have a net worth of $1.8M but they are much more easily able to shift financial resources aound to meet their needs.