Will he? Yes. Should he? Yes. The fact that he hasn't yet isn't statistically notable. The chances he would have used a challenge based on the rate coaches across the league are challenging calls is around 50%. In other words, it's a non-issue. If he's 0-for-20, I can get on this bandwagon with you to
DPG. For now, it's an insignificant observation.
According to you, you'd challenge even if it had a 10% chance of being successful. That means you are valuing timeouts at about .5 points -- and that's assuming every successful challenge results in a 4-6 point swing.
BTW, a 6-point swing? You're banking on challenging made threes and hitting threes on the other end? That's a bold assumption coming from a Spurs fan