BNB, or Binance Coin, has become expensive due to several factors. One main reason is the increasing popularity of the Binance exchange, which has driven up demand for BNB as users need it to pay for trading fees, participate in token sales, and access various services on the platform. Additionally, BNB offers utility and benefits within the Binance ecosystem, such as discounts on trading fees, further increasing its value and demand. Finally, like most cryptocurrencies, BNB's price is also influenced by market speculation and investor interest, which can lead to price appreciation.