It exists because mentoring has an ordering problem. Invoice afterwards and the mentor carries the risk of not being paid; take payment upfront with no protection and the mentee carries the risk of not being served. Escrow removes the choice by taking the money out of both parties' hands in between.
The second thing it removes is the conversation. When payment settles at booking, the commercial discussion happens once, before any work, rather than as a follow-up email after a session that went well. For a mentor that is the difference between a practice and a collections job.
Escrow is also what makes a cancellation policy enforceable. If funds are already held, a late cancellation can settle against the mentor's stated terms automatically, instead of requiring the mentor to ask for money for a session that did not happen.
Mentor10
On Mentor10 the mentee pays when they book, funds are held by a regulated payment partner until delivery, and payouts land on a predictable schedule in the mentor's own currency. The mentor never sends a reminder.