Because the current battery technology means that batteries are very heavy and the range very limited.
Also, at the low capacity end of the market, they are far too expensive.
Electric vehicles are probably just a partial short term help, the future is probably hydrogen powered vehicles, which produce water vapour as exhaust gas.
Current internal combustion engines could be converted relatively easily to run on hydrogen – many cars have been converted to run on both petrol and LPG.
British Superbike School 