Why do some Escorts charge more then double their rate for twice the amount of time

For example lets say an Escort charges €80 for a half an hour of her time but charges €170/€180 for an hour? - Meaning theres an extra 10-20euro added to the second half of the session.

One would assume it would be €80x2 - €160 but in some Escorts prices this isn't the case.

I'm generally just curious as to the reasoning behind it.

Is it to deter clients from 1 hour sessions as the Escort prefers the 30min sessions, or maybe to deter the bargain hunters from the more generous?

Would love to hear your thoughts on this both Clients and Escorts.