its been explained a million times that if you coerce people to lock funds up for 3 months and not make any transaction onchain... they no longer need to actively have a fullnode because they no longer care about what happens onchain because the lock is doing its job
people using LN are not carrying their desktop pc to starbucks to monitor the blockchain. they are using phone apps. meaning again. not having a full node active
thus LN causes less decentralisation as in the end the only fullnodes left become the custodial services and 'factory' services of LN
What makes you think that people will shut down their existing full nodes (think the ones that are active on Bitnodes right now) to run an LN channel? If anything, it's going to be the new users who only run LN channels, not OG's who were already running full nodes before mass LN channel creation by other users.