Cost is also a factor. A modern natural gas furnace is 90+% efficient and even an older one is going to be above 50%. When natural gas is 1/7 the cost of electricity that 50% efficiency is still 1/3 the cost. There’s an argument for using a space heater to heat just the occupied portion of the home, but at 3-6 times the cost of gas ones often just as far ahead to keep the furnace going. On that note, even if the heat pump gets a COP of 3 like your example, that’s still twice the cost of gas for the amount of heat put in the house and 3+ times the cost to install a proper ground loop and heat pump vs a gas furnace.

I suspect part of the issue though is shitty rental units that don’t give the tenant control of their heat and/or the landlord pays gas but passes off electricity on the tenant. Also. If it’s a poorly done build you can get things like the HVAC not being designed to match the floor plan, so you end up with some rooms being cooler and people supplement with electric heat.