I guess for the same reason you can't buy bikes with downtube shifters anymore. The manufacturers put on what the majority of the buyers would want and the minority has to customize if they want something different.
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If once a man indulges himself in murder, very soon he comes to think little of robbing; and from robbing he comes next to drinking and Sabbath-breaking, and from that to incivility and procrastination.
- Thomas De Quincey