Hi, I'm Harvie from MoonSwap. And i hope i can help you.
MoonSwap runs on conlfux, and we treat conflux as Ethereum Layer2, so users who hold Ethereum assets can enjoy high speed and 0 gas experience on MoonSwap.
In fact, our users need both confluxportal and metamask. And ERC777 token can be traded on MoonSwap. When you migrate ERC20 assets to Conflux, ERC20 assets will be converted into corresponding ERC777 assets, which is cToken. For example, if you migrate ETH to Conflux, they will become cETH. ETH and cETH have the same value and can be converted to each other at any time.
I reckon it’s because Moonswap is actually supported by Conflux so they probably have some kind of exclusive partnership. Even though not having Metamask means losing quite many users, I think.