Why gas prices change
Block space is limited. When many people want to transact at once, during a token launch or a market crash, they bid up the fee. Complex actions like DeFi swaps use more gas than simple transfers.
How to pay less
Send transactions when the network is quiet, use layer 2 networks such as Arbitrum, Base or Optimism, where fees are often a few cents, and check a gas tracker before big transactions.