Multiple reasons:

1) It IS inherently cleaner than conventional even without a major switchover, for two reasons:

. a) A central power station can be much more efficient than a small internal combustion engine, even using the same fuel. A good natural gas power station can get above 60% efficiency (caveat: LHV... but even using HHV value for natural gas, still above 50%), whereas internal combustion engines are around 15-25%, although can be even worse. This difference is much greater than any transmission or round-trip charging losses.

. b) Regenerative braking only (practically) works with electricity. This already makes electric cars cleaner, since they can recapture kinetic energy while braking. In conventional cars, this is all wasted as heat. A side benefit of this is electric car brakes last way longer.

2) We ARE changing over. Coal used to be >50% of our electricity, now it's on the order of 30%, and usually is dwarfed by natural gas at 33%. Natural gas per unit /thermal/ energy gives off a lot less CO2 than coal and still significantly less than gasoline or diesel. And natural gas plants are also very clean burning with almost no ash and soot (which can cause global warming in other ways, besides asthma and lung cancer, etc). And it's easier to make really thermally efficient natural gas plants than it is for coal. HOWEVER, even natural gas is now over-shadowed by clean energy (now at 36% of power) from nuclear, wind, hydro, solar, and geothermal combined (in that order). So now over a third of electricity is essentially carbon-free. This means that electricity on average is actually less carbon intensive in the US than if it were all produced from natural gas alone, which makes it even cleaner than if it were all centrally-burned petroleum, which makes it cleaner than if it were small internal combustion engines.

3) Fuel cells (let's take hydrogen for example) have major problems. The MAIN being the terrible round-trip efficiency. Electrolysis of hydrogen from water using electricity (this is basically the best case scenario, realistically) is 40-60% efficient. Fuel cells are themselves only 40-60% efficient. Then you add in the significant amount of energy needed to compress and transport the hydrogen (transportation is comparable to transmission losses from electricity, but sometimes worse), and the total efficiency is somewhere between 20-35%. Batteries are around 80-90+% efficient, and you can do even better if you're careful. That means you're ALREADY only able to travel a fourth to a third the distance in a fuel cell car for the same amount of electricity generated. That's insanely bad when you think of it. This is the main problem.

4) Fuel cells are actually much more expensive. They require high pressure storage and transfer. The fuel cells themselves are expensive, too.

5) Hydrogen itself has problems. There are material compatibility issues. A good lithium ion battery using a silicon chemistry can actually have a higher volumetric energy density (when you include the lower efficiency of fuel cells) than hydrogen, meaning you can make a more compact electric car or put a bigger battery in the same space. Hydrogen is also insanely flammable, with a very high flammability range in air. It makes explosive mixtures with air very easily. It also causes embrittlement of metals.

6) Electricity distribution is already ubiquitious due to the electric grid. Most people can charge at home (and even more if apartments just run out an outdoor outlet to parking spaces). That means people almost never need to go out to a filling station. It's only needed on long trips, and even then only after exhausting the internal battery. Many hotels/motels already have RV charging (and many allow EV charging), so on a multiday trip could start out each day with a full "tank" without any trips at all. And there's already been a lot of work installing charging stations all over the country, including very fast charging roughly equivalent to the typical hydrogen filling station. It's a lot cheaper to install a fast electric charging station than a hydrogen filling station and a lot fewer are needed.

7) Almost all hydrogen is produced by fossil fuels using steam reformation. Hydrogen is even LESS of an "inherently clean" technology than electric is, if you use today's energy mix for both!

8) Electric cars are incredibly simple. Even a conventional car already includes a battery, a starter, and an alternator. In an electric car, you combine the starter and alternator into a single larger device, get a bigger battery with cooling, and throw the entire rest of the engine (spark plugs, pistons, camshaft, exhaust, catalytic converter, fuel pump, oil pump, oil sump, oil filter, fuel filter, fuel tank, air intake, air filter, etc, etc) away. You also can DRAMATICALLY simplify the gearing. As you mention, electric cars are cheaper to develop. But they're also cheaper to make and much cheaper to maintain. Additionally, a hydrogen fuel cell car will already need everything an electric car needs, including a (smaller) lithium ion battery.

9) The ONLY thing really holding them back is battery cost. And that is rapidly being solved. A >200 mile battery gives you a practical range, very long battery life (hundreds of thousands of miles), and ability to accept a very high charge rate. And this is actually something we'll want anyway to make the grid more effective (get rid of expensive peaker plants and local grid bottlenecks at high usage) and to allow higher penetration of solar and wind. If we build out our battery production facility for electric cars to be ubiquitous, we've basically also completed enough battery production capacity to go, say, 80% solar/wind. (Although for the love of all things holy, let's keep at least our existing nuclear power plants running until we've gotten rid of coal and gas.)