Some cryptocurrencies, despite their decentralization, raise some sort of transaction fees within their Blockchain. The motives behind this are different as every project has other token metrics and a specific token model. Nevertheless, most people pay transaction fees to transfer coins/tokens off from exchanges as the popular ones are centralized and profit-oriented companies. They charge certain commission fees for administrating the accounts and guaranteeing a certain security standard. It is important to understand that transaction fees vary from exchange to exchange. Generally, bigger exchanges liken Coinbase or Binance have slightly higher transaction fees due to good reputation.