They didn't answer their own question. The real reason is that "B" batteries had higher voltage (~45V) needed for plate voltage in vacuum tube radios. "C" cells were originally for tube biasing. "A" cells were for the tube filaments (heaters). Transistorized electronics can work at lower voltages, don't have filaments, and don't need a separate bias supply. Sorry so technical, but it is the only reason we no longer have "B" battreies.
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