I have withdrawn and trade ETH from MEXC multiple times already and I am never charged more than $3 but when I swap ETH ERC 20 on Uniswap the gas fee is almost always $10 and few times over $10, why is it like this? Are DEXs suppose to be more costly normal centralized exchanges?
Decentralized exchanges are not made for exchanges of small amounts. The main difference is that with a decentralized exchange, an actual transaction takes place on the blockchain. And this costs (a lot), depending on the chain. The fees are usually even higher because the transaction has to take place within a short period of time. The fees are relatively high for Eth and Bitcoin in particular. However, there have also been phases with ETH where you pay up to $100 for a transaction on Uniswap. With centralized exchanges, there is no actual blockchain transaction during the exchange. Only the amount is deducted from one user in a database and credited to the other. The costs are therefore significantly lower.