Because full node don't enforce SegWit address for now.
SegWit is needed (must be enforced) for Lightining Network.
https://bitcoincore.org/en/2016/10/27/segwit-upgrade-guide/
If enough miners do decide to adopt segwit, it will eventually activate and wallet users will be able to begin creating transactions with segregated witnesses. The segwit soft fork has also been designed to be both backwards and forwards compatible with all commonly-used wallets, so wallet developers and users can also independently decide whether they want to adopt segwit or continue making transactions without segregated witnesses.