There's a few reasons for this, firstly the rear-visibility of an F1 car is abysmal. I mean just ridiculously bad. The only tools drivers have for seeing behind them are the wing mirrors, the size and positioning of which is (as much as the rules allow) completely driven by aerodynamic concerns and what little viewing they can provide is going to be optimised towards giving the driver information useful in a racing context not for doing a three point turn.
Secondly the regular turning circle (i.e. when you aren't "spinning" the car around) of an F1 car is huge because the cars and their steering aren't designed for making very tight turns (because doing so would harm performance in the sorts of turns you see on race tracks), you only have to look at how they struggle around Lowes hairpin at Monaco to see that for yourself.
Finally you've got the extra time it takes to change into (and out of) reverse gear - remember that F1 gearboxes are sequential dual-clutch transmissions designed for going up and down the gears between 1-8 as fast as possible so to get into reverse the driver has to get the 'box into neutral, engage reverse and then do the opposite to get back into a forward gear.
All of this means reversing out of an escape road or similar is not only more difficult and more hazardous then the spin approach but crucially it takes far longer which is why you'll only see them reversing when they really have to.