I think this question is based on the assumption that escorts are "too tired after the day" from engaging in sex professionally.
but what about the many other options.. what if they have sex first thing in the morning with their casual partner or husband or girlfriend etc (for free) before they see a client
or perhaps they don't make appointments 7 days a week
or maybe they sometimes are and sometimes aren't up for sex with their partner on days that they see a client.. because some clients leave them with lots of sexual energy and some do not.
not all sex (for free) is recreational for escorts.. sometimes it is significant emotional comfort, part of a deep connection, or the fulfillment of certain needs they have that aren't part met by their professional escorting.