Unfortunately monetary reasons are limiting us from using Li batteries in all applications at the moment.
The world IS indeed moving in the direction of Li battery technology, but it's only been ~10 years since Li batteries starting taking off.
But eesh, you should have seen how expensive the buggers used to be.. **** near 60% less nowadays, but still unfathomably expensive if they were to be used for hardcore audio systems, as the more abuse the battery needs to take, of course the price follows.