Because it depends on how much these providers charge, some have a fixed amount based on number of recipients, some just take their percent for each point - the paperwork, the transfer, taxation, etc. Also depends on the used transfer method, some may take 30% only because of the used payment method. The resulted costs should be covered, right?
So, from what they should be covered? They also usually charge both sides!
For example, my provider charge me $10 for SWIFT + some almost random sum by banks in between. With payout of $15 it will be madness, and if I choose a stablecoin, I will be charged up to 20% depending on the moon phase.