This can be understood that because the fundoshi is a niche item that the major undergarment manufacturers cannot easily embarked on the production with the following reasons, the undergarment cannot be traded on the major distribution network, and thus it's rare to find them in stores.
これは以下のような理由から大手下着製造業者が積極的に手掛けにくいニッチ商品であることが、大手流通網に乗らず、広く店頭に並ばない理由と推測される。