Any car with a combustion engine produces lots of waste heat as a byproduct. That's why cars need radiators to throw off the excess heat. So tapping into that excess heat to help heat the car interior in the Winter is simple using a heat exchanger. This is also why if you are ever in a car that's overheating in the Summer and you can't pull over, turn on the heat. It's not very pleasant for the passengers, but it will help extract the excess heat from the engine.
A battery powered car on the other hand produces virtually zero heat, since all the energy is very "efficiently" converted to motive power. Need heat? The only available energy source is the battery and using a battery to generate heat is expensive power-wise. The situation is made worse in Winter in that batteries, running essentially chemical reactions, are less efficient in cold temperatures, since many/most chemical reactions run slower when cooled.
Makes perfect sense; thanks.