It's one of many ways to remove connection/link of your past Bitcoin activity. And while it's true the fees is high, few people use this method either by doing it manually or use mixer which claim to do that for you.
What's the difference between sending 1 BTC to mixer and receiving 0.096 BTC from mixer compared to sending 1BTC to mixer, converting it in 226 Monero, then converting 226 monero and receiving 0.096 BTC. What's the difference? I send bitcoin and receive bitcoin. If it's an instant exchange or withing 24 hour timeframe, I think it doesn't make much sense.
Some people say it's harder to track, especially if you 2 different exchange (BTC to XMR and XMR to BTC) where each exchange have different customer and addresses.