Can’t you just break down water, use the hydrogen to power the electric motor, and I don’t think O2 as a byproduct is bad, now this is of course an ideal condition, but why hasn’t this been looked into more?
Because it will always take more energy to break the water than you will get burning the Hydrogen in Oxygen back into water - it's basic thermodynamics.
You will lose some energy as heat that you cannot get back*.
You can't power a car from a process that loses energy. Even if you use a battery to donate the lost energy, then you might as well just cut out the lossy middleman and just run off the battery or generate the Hydrogen elsewhere - which is what we currently do.
It is better to think of Hydrogen as an energy transporter than as a fuel, as you'd need to generate the Hydrogen somewhere that has abundant energy (ideally renewable), then transport I where needed, such as a Hydrogen powered generator.
*Interestingly the fact that all processes generate waste heat means the only theoretically 100% energy efficient process is heat generation itself, as all forms of energy eventually degrade to heat (as it is essentially the universe's waste energy).