In theory: because it has no open source decentralized wallets available that are good for everyday users and when it's been out this long, that probably means it's designed not to allow such a wallet to be made

In practice: because, unlike open, decentralized cryptocurrencies like Bitcoin / doggie coin / Monero, people post all the time about losing money in Lightning, having transactions fail, needing to waste endless hours troubleshooting etc., just like you'd expect from a service with no open source decentralized apps