In some cases in some jurisdictions because their bank threatens to close banking access if they accept Bitcoin. In some countries it is declared by government that using Bitcoin as a MoE is outlawed- generally more autocratic countries like China, Turkey, Russia and Thailand. In other cases so few people want to pay with Bitcoin or even know how to that businesses give up. It still takes a relatively motivated, principled and courageous business to accept Bitcoin. Often one prepared to risk the wrath of bankers and governments.