Feel free to be cynical in your answer, but why would a property owner who just paid a fortune to buy a single family house in SF want to rezone the neighborhoo

Feel free to be cynical in your answer, but why would a property owner who just paid a fortune to buy a single family house in SF want to rezone the neighborhood to see a large apartment complex built next door? Now that they've paid the heavy toll, they stand to lose the most.