Thiem using Pure Strike

I mean, it's not like the Pure STrike is even that good. Maybe it's just me, but it lacks power and stability. Maybe these cons are negated by Thiem's huge forehand. Is that the reason for his gigantic backswings, or does he use the Pure Strike because of his gigantic back swings. With, say, a pure aero, his shots might just fly out. Is it that he likes it's manuverability?
Sorry for all the spelling mistakes, I dont want to go back and fix them.. too lazy.