@Caroline1810 You are a bit confused. Hosts who use channel managers can opt to use the "Host only service fee" option. In that case, instead of the guest seeing a separate service fee charge, it's all included in the nightly price.
So those hosts would have had to up their nightly price, because they will now be paying Airbnb both the host service fee of 3% plus the guest service fee.
The guest ends up paying the same in total, a guest service fee just doesn't appear as a separate line item. It's basically just a marketing gimmick.
It's like when you book a hotel, you don't get charged a separate cleaning fee, as a guest would on Airbnb. But that doesn't mean the hotel owner is paying for cleaning out of his own pocket- cleaning, hotel security, 24 hour reception, etc, is all factored in to the nightly price the guest pays.