The registration fee that is paid to the ens dao varies on length. Shorter names are much more expensive. But for 5 characters or more, its 'only' $5 per year. What is expensive is the gas fees to claim the name, mint the NFT to complete the registration, and then set a reverse resolver for it. Even at lowish gas fees it can be $50-$100.
Because rollups exist on Ethereum that are cheap and are far more suited to end user self-custody then lightning ever can be. At the moment zk-rollups are roughly 100x cheaper then mainnet, don't require the user to run a node to self custody, and the user can force a withdrawal to mainnet even if the roll-up operator completely dies.