"Bitcoin Unlimited" has no maximum block size, hence the name.
There are many problems which arise from unbounded transaction rates in Bitcoin. The most fundamental is that long term the coinbase reward is zero, and transaction fees are the only reason to create new blocks. Without artificial scarcity of block space (artificial in the sense of beyond what hardware can support) transaction fees would tend to zero, and mining would no longer generate revenue.
LN is proposed to allow many users and many transactions (when nodes cooperate) while keeping the security properties of Bitcoin (when nodes don't).
There are many problems which arise from unbounded transaction rates in Bitcoin. The most fundamental is that long term the coinbase reward is zero, and transaction fees are the only reason to create new blocks. Without artificial scarcity of block space (artificial in the sense of beyond what hardware can support) transaction fees would tend to zero, and mining would no longer generate revenue.
LN is proposed to allow many users and many transactions (when nodes cooperate) while keeping the security properties of Bitcoin (when nodes don't).