Electric heat, although very efficient in terms of the total amount of energy converted to heat, essentially 100 percent, it's still electric heat and as such demands lots of power.
But dumping high-quality energy (mechanical or electrical) is terribly wasteful, even if the conversion is perfect. The reason is that, in going from heat energy to high-quality energy you lost 2/3 to 3/4th of the heat - and all you get back is that last quarter or so.
If you use that high-quality energy to run a heat pump you can work that multiplier the other way, and get perhaps three times the heat for a given amount of power by using the high-quality energy to pump some available heat from outside to inside - BEFORE you dump that good stuff as heat, too. (Exact amount of your multiplier depends on the efficiency of your heat pump and the temperature difference you're pumping heat across.)
That's why, if you're burning fuel, you use it to heat your house or water directly (or when it comes out of the heat engine that's grabbing that quarter or so you can get out of it as high-quality energy), rather than generating electricity with it and using the electricity to make your heat. Why throw 3/4 away when you're PAYING for it - via a utility company or directly?
It's also why, if you're doing solar heating, you use the sun to heat your working fluid rather than to generate electricity to burn into heat. That square yard of solar surface can get you a kilowatt of heat or a couple hundred watts of juice - and it's cheaper to collect it as heat, too. The only time you should be making heat with photovoltaic is when you have to dump it anyway to keep from overcharging, or for small or short-term uses where control is paramount (like soldering irons, hair driers, or microwave ovens.)
(Wind is another matter: Sometimes there's SO much available that it makes sense to use it for heat, and you tend to get more when you need more heat. Usually it's like photovoltaic, though: Too little available, or too expensive to grab it, to use for electric heat. Heat things opportunistically with your dump loads and let it go at that.)