Ethereum predates the ERC-20 token standard, which was introduced to standardize token creation on the blockchain. Since ETH doesn't conform to this standard, it cannot be directly used in many decentralized applications that rely on ERC-20 tokens. WETH solves this problem by allowing ETH holders to wrap their ETH into an ERC-20 compatible token that can be used across a wide range of DeFi protocols and dApps.
WETH essentially bridges the gap between ETH and the broader ERC-20 ecosystem, allowing ETH to function seamlessly in DeFi, token swaps, and other smart contract interactions.