I see.

Yes, even in this bear market, there are times of the day that bitcoin network on-chain trx fees can pop over $1 or $2 even, to get into the next block. And not all wallets have RBF support (or don't have it enabled by default), so it could make for a very long wait for a BTC transaction to confirm (as the exchanger takes a risk giving you BTC after accepting your BTC without any confirmations). LTC block confirmation time is shorter (average of 2.5 minutes), so that, in addition to LTC network trx fees being trivially low (at current volumes), I can see why an exchange operator would offer to take LTC.

This helps to explain why most shitcoin exchanges don't (yet) support Lightning network and at the same time charge a high fee for on-chain bitcoin withdrawals. Rather than sending those bitcoin off the platform, that high fee helps convince customers to convert their BTC to a shitcoin (in which the exchange earns their trading fee, and provides liquidity for shitcoin traders), and then the customer withdraws the shitcoin. So LN does, in effect, result in less trading fees earned by the shitcoin exchanges.

Because if, in your example, you had LN and would gladly have used LN to pay as it would have been an instant transaction (no confirmation), and fees at a trivial level.