The challenge for the Lightning Network is cheaply routing payments from consumers to merchants. LN is optimized for anyone-to-anyone payments, while in a real economy money moves from consumer to merchant to producer to worker (consumer). LN is not optimized for this circular pattern, where many consumers pay a single merchant.
Also, everything is done via two-way payment channels in LN, which means that you need to lock X BTC in a channel in order to send it, which becomes very capital intensive for nodes close to merchants who need to lock millions of dollars worth of bitcoins to cover merchants’ monthly turnover (this is in addition to the BTC locked up by other nodes who participate in the transfer but are not directly connected to merchants). If you want to send 0.1 BTC through 10 nodes, each of these 10 nodes must have locked up 0.1 BTC on the blockchain, and you’ll pay blockchain fees if just a single channel/node in your path doesn’t have at least as much as you need to send.
A proper payment network needs two different types of nodes: senders and receivers. Using a single type of node for both doesn’t make much sense, since merchants and consumers have completely different needs. Senders need to be able to send relatively small amounts relatively frequently (a consumer making a few purchases per day), while receivers (merchants) need to redeem relatively large amounts (e.g. one week’s worth of payments) relatively rarely for bitcoins (on the blockchain).
