As read in our article ETH Fees, Gas, & The Halting Problem, "in Ethereum, “Gas” is a computational unit or a measure of the number of resources needed to execute a smart contract on the Ethereum Virtual Machine (EVM).
Some smart contracts require the EVM to use more resources to execute than others.
Because of this variation, some transactions and programs need to pay more or less in fees than others.
The less resources (computation, storage) your program requires to execute, the less ETH you’ll need to pay the miners."
This Ethereum network policy applies not only to Edge Wallet but to every wallet able to manage Ethereum tokens.
Please note that this policy applies to exchanges, if you want to exchange an ERC20 token to another coin (for example USDT to ETH), you need some ETH to cover the mining fees, because the exchange needs an Ethereum transaction.
As you can see, even if we have funds in USDT, we cannot send them because we need ETH to cover the fees (gas).
How to change the fees and set a custom fee
So, for example, you could need a Limit of 200,000 and a GWEI value of 50, if this is the Standard value you see on EthGasStation.
Fees for ETH transfers usually have a limit of 21,000 but a limit up to 80,000 can be necessary. GWEI value have to be set according to https://ethgasstation.info/
So, for example, you could need a Limit of 80,000 and a GWEI value of 50, if this is the Standard value you see on EthGasStation.
This is true for simple transactions (Ethereum to Ethereum address), but also for exchange (for example Ethereum to Bitcoin) and especially for token transfers, that, as we saw above, are complex smart contracts.