1. All payments have to be routed across channels of arbitrary size across an arbitrary network. It's a small travelling salesman problem that only gets worse as the network increases in size.

2. It requires a transaction to L1 to open/close a channel. If 1B+ people used it the Bitcoin network itself couldn't cope with that. At 7tps it can handle a max of 220M transactions per year.

3. You need enough liquidity in all channels to your destination to send a payment. This is fine for micro transactions but it can't handle $1k+ transactions well at all.

4. You have to re-balance channels or they stop working.

5. You need some sort of watchtower / guardian node to prevent the other person from being able to steal your funds.

ZK-Rollups completely obsolete the lightning network. If Bitcoin did a hard fork to make them possible every single person would migrate to them. Lightning is not a long term solution, it's mostly a meme to throw back at people who say Bitcoin doesn't scale.

One thing I don’t like about the protocol is that LN nodes must stay online or risk having the other parties of their channels steal their funds. I know there are watchtower services to help guard against this but needing to trust a 3rd party to make sure you don’t lose your money goes against trustlessness, a core principle of cryptocurrencies. This is the reason I abandoned the idea of running my own LN node. I didn’t want to risk losing money in the case of an extended outage of my node.