To talk about maximizing glide ratio is the same as talking of maximizing Lift/Drag (derivation can be given, "exercise for the reader"). Since lift is a given when gliding (we don't typically lose weight when engines are inoperative - and we consider a steady symmetric flight). To maximize L/D we minimize the drag.
For a car, or other land based vehicle (car, train etc) this typically means we move as slow as possible.
An aircraft has a different drag profile. Due to the fact that the wing doesn't generate work, bending the airflow downwards also means it has lower horizontal relative velocity (airflow stays same total relative velocity). Thus the lift vector is slightly backwards.
This is the lift-induced-drag. And since at higher velocity we need to bend the air less (more volume of air is moving per unit time), this drag reduces with velocity.
This leads to an image like below:

Now the equation for the drag coefficient is written like:
$$C_D = C_{D_0} + \frac{C_L^2}{\pi AR e}$$
(With $C_L$ being the lift coefficient, $e$ efficiency span factor which counts for winglets etc and $AR$ the aspect ratio of the craft). And $C_{D_0}$ the sum of all parasitic drags.
We are typically quite good at reducing skin-parasite drag. So designing an aircraft for a higher velocity means a better design. Another thing to note is that a higher aspect ratio makes a more efficient gliding craft => hence gliders have long slender wings.
However this would be equal for both props and fan/jet craft. What makes a fundamental difference is another form of parasitic drag: wave drag. Wave drag is massive compared to the other forms of drag. And it happens where (locally) the relative velocity with air is above mach 1. (IE on top of the wing, where curvature is maximum you typically have highest velocity). A propeller is moving not only as fast as the aircraft, but is also adding another rotating component, so the tips of a propeller have a higher relative velocity than the rest of the aircraft. Where a fan engine typically has an inlet designed to slow down the incoming airflow, so that the relative speed isn't above mach 1.
For this reason a turbo-prop has to be designed to cruise at lower mach number. This that cruising is less efficient. So picking a propelor as your initial design strategy means you design an aircraft where aerodynamic efficiency is not a main design parameter. Maybe landing/takeof distance is more important, or cheap production/maintenance is a driving parameter.
Since aerodynamics isn't a main parameter it will show in the L/D curve.
If glide performance with paramount I'm sure one could design a very efficient propelor craft, props typically can rotate the blades anyways, so you could at "power off" easily design those to give minimal drag.
It's just not really something to consider.