Am curious why bitcoin doesn't want to increase it's block size from 1mb ?
Comparably to the rest, I'll have to disagree with the common opinion, that the Bitcoin network can't handle larger blocks. The main reason I see, is that increasing the block size breaks backwards compatibility.
Price should be high and stable enough to make it profitable for miners and less costly for nodes.
Completely your opinion. Price is high enough apparently; difficulty is in ATHs lots of months now. Also, running a node is cheap enough.
Doesn't LN using third party affect bitcoin Decentralization ?
Depends on what third party you mean. Third parties like BlueWallet or Wallet of Satoshi that act as middlemen, do indeed hurt, not only decentralization, but in the ability to control custody of your funds.
Also is setting up a LN complex? And does it work well for low Transactions?
It is complex, in comparison with a simple on-chain wallet like Electrum. Yes, it works well for low-value transactions; in fact, it's specially designed for those.