But payment channels, and their capacity, are actually limited by how much Bitcoin the people who run nodes hold, are limited by how much capital they want to open payment channels with, are limited with their technical-skills in how to maintain the node/balance channels.
That limitation, and increase in demand for LN transactions = higher fees?
Let's compare it to
Tether for a moment: it's 24h volume is more than twice it's market cap. Each coin is "used" several times per day. The same will happen for LN-nodes, and the same happens with actual dollar coins and banknotes too.