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.
again custodians and SERVICES that centralise liquidity and have customers. would be the full nodes
but USERs that just want to spend their value will lock up their funds. and then play around on litewallet phone apps.. why.. because carrying around a desktop for the full node is heavy. the locks mean no need to monitor the blockchain every minute. and not spending funds on chain mean no need to watch the blockchain for new income
so here is the question reversed onto you
newbie average joe just getting into crypto why would they go full node? if they are being told the way forward is microchannel altnets
think about it. most exchanges will offer channel opening facility with balance instead of withdrawing to a mainnet. to then lock to then open a channel. so most new users will just do that for convenience and most exchanges would sway users into that convenient way.
so ask yourself who would choose to start a full node when all the utopian altnetters are pushing hard telling people to not use bitcoins main net