The reason why SE probably did this is simple. They are aware that people are selling their houses for double/triple/quadrupole the price. Doing this would only give them more money in the process, Support more people buying multiple houses(with alts etc)

They should just make it like this, Your main character is allowed to have one single house(Personal) All their other characters are automaticly co-tenants(Not to be confused with tenants you chose yourself)