Kinda like asking why isn't there a single "best" brand of car. The answer is fairly obvious in that "best" is hugely subjective and governed by many variables

Kinda like asking why isn't there a single "best" brand of car. The answer is fairly obvious in that "best" is hugely subjective and governed by many variables including a particular individual's needs or preferences. This gives rise to many "local maxima" in the subjective preference function, allowing a variety of car types to exist.