The network itself is very centralized.

"if the 100 routers with the highest simulated traffic increased their transaction fees to close to on-chain fees, the majority of payment sources would have no less expensive option to route their payments."

https://arxiv.org/abs/1911.09432

"90% of the nodes only correspond to 10% of the cumulative betweenness of all nodes. Consequently, this indicates an extraordinarily high network centralization, where 90% of the shortest paths in the network lead through only a few highly centralized nodes"

https://arxiv.org/abs/2201.07746