> I think this is a bad move, since security is more than enough.
Security isn't/wasn't the concern, the trade-offs exist to ensure verifiability in the most trustless way possible (low hardware and bandwidth requirements). This enables a decentralized system which is open to any participant and keeps miners accountable. If running a node is limited to miners and exchanges and requires a renting server racks there is just no point.
> Lightning is not viable, because it requires "watchtowers" to check for early state commit attacks
This is inaccurate. LN has shortcomings currently but this isn't one. Without a watchtower your peer in a channel can force close it while you are offline by publishing an outdated state on-chain and attempt to defraud you, but if at any point before the end of the grace period (usually ~2 weeks) you are online and you produce a more recent state you get the whole balance of this channel back (this is how dishonest peers are punished). This is one channel mechanism (Poon-Dryja), another mechanism (Eltoo) which doesn't require as much monitoring/penalties will eventually come but depends on changes to Bitcoin protocol which are still pending.
Secondly theses optional watchtowers which automate this process minimize trust a lot as they can only publish the most updated state IF and ONLY IF the counterparty in your channel published their outdated state. So they have no real custody of your funds.
Lastly solutions like local federations (Fedi to name one) can address your concern of people not being able to run servers, if the users aren't content with the public offers of existing watchtowers.
> But, for instance, Bitcoin Cash has larger blocks (the reason for the first fork of Bitcoin). However, in spite of its technical advantages, adoption severely lagged compared to Bitcoin. I wonder why that is.
Because having larger blocks is not a technical advantage if your goals are the principles mentioned in the first paragraph. If you intent to compromise on these then just build a centralized database, it will be more efficient and at least you won't lie to people pretending that your system is open/decentralized (like Bcash supporters do).
Security isn't/wasn't the concern, the trade-offs exist to ensure verifiability in the most trustless way possible (low hardware and bandwidth requirements). This enables a decentralized system which is open to any participant and keeps miners accountable. If running a node is limited to miners and exchanges and requires a renting server racks there is just no point.
> Lightning is not viable, because it requires "watchtowers" to check for early state commit attacks
This is inaccurate. LN has shortcomings currently but this isn't one. Without a watchtower your peer in a channel can force close it while you are offline by publishing an outdated state on-chain and attempt to defraud you, but if at any point before the end of the grace period (usually ~2 weeks) you are online and you produce a more recent state you get the whole balance of this channel back (this is how dishonest peers are punished). This is one channel mechanism (Poon-Dryja), another mechanism (Eltoo) which doesn't require as much monitoring/penalties will eventually come but depends on changes to Bitcoin protocol which are still pending.
Secondly theses optional watchtowers which automate this process minimize trust a lot as they can only publish the most updated state IF and ONLY IF the counterparty in your channel published their outdated state. So they have no real custody of your funds.
Lastly solutions like local federations (Fedi to name one) can address your concern of people not being able to run servers, if the users aren't content with the public offers of existing watchtowers.
> But, for instance, Bitcoin Cash has larger blocks (the reason for the first fork of Bitcoin). However, in spite of its technical advantages, adoption severely lagged compared to Bitcoin. I wonder why that is.
Because having larger blocks is not a technical advantage if your goals are the principles mentioned in the first paragraph. If you intent to compromise on these then just build a centralized database, it will be more efficient and at least you won't lie to people pretending that your system is open/decentralized (like Bcash supporters do).