Because moving a family of four is extremely disruptive for everyone, and it's very rare to have more than a year's security with a lease, even with a good relationship with the landlord. Not only that, but if your kids are school age, there's serious pressure to find a new rental in the same school area, which makes shopping for a new home that much harder.

>>and it's very rare to have more than a year's security with a lease, even with a good relationship with the landlord.

Huh? Landlords prefer stability as much as tenants. Very rarely will they say no to a multi-year lease. They may want to add the option of rent re-evaluation after the first year, but from a landlord's perspective it is very difficult to find good tenants, therefore the longer those tenants stay the better.

No landlord I have ever had has ever agreed to a 2-year lease. There's no "huh" about this point: if you rent, your tenancy continues at the pleasure of the landlord. That's not a fun place to be if it's important to you to provide a stable address for your kids for the next 10 years --- and that is usually pretty important.

It's kind of a joke or a proverb I guess since both houses and funds are investments with a certain risk but houses also double as a place where you and your family can live ;-)