Electricity is a lot cheaper and _can_ be produced clean (wind, water) or cleaner (nucleair) or a bit cleaner (gas) or not so clean (coal) compared to petrol.
Besides this, an electrical engine is _much_ more efficient compared to petrol/diesel engines. A petrol/diesel engine turns it's fuel into about 30/40% motion, the rest is heat that it produces.
An electrical engine is in the 80/90% range and runs much cooler.
It's also infinitely more elegant and simple in design and maintenance.
In my work I sometimes run into sprinkler systems and I always love to see the electrical pump:

which is so small elegant, simple and efficient, and then next to it is the diesel/petrol pump, which seems (and is !) extremely complicated, inefficient NOISY and clumsy compared to the electrical one:

Sprinkler pumps need to be tested every 2 weeks. This is mainly because of the relative unreliability of the diesel/petrol pump.
The ONLY benefit it has is that it will run when the mains fail, and that's also the only reason they need to be there.
With cars, the big problem will stay range. But I'm convinced we are seeing the beginning of the end of the traditional engines. And it's about time.