in a high fee environment, users can be priced out of transacting on the base chain, as they cannot afford the transaction fees.
they may try to onboard to layer 2 (LN), only to discover that they are still subject to layer 1 transaction fees, for the purposes of opening, splicing/balancing and closing channels. (they must also hold sufficient balance to broadcast a recent state transaction, should their channel counterparty attempt to force-close / cheat them).

as fees rise considerably, if a user cannot afford to transact using non-custodial layer 1, there is a strong possiblity that they will also be unable to afford non-custodial layer 2. 

those who can afford the fees will benefit from increased transaction throughput (on layer 2), however layer 2 does not solve the problem of high fees, and thus scales the overall userbase only marginally.