Ablative is also used in terms of the mechanism of carrying away the heat with the evaporating material. A non-ablative heat shield like the space shuttle's just takes a lot of energy to heat up but will still carry all that energy with it and it'll slowly diffuse into connected components (that then heat up a lot due to their lower specific heat capacity).

Edit: I didn't think of space but in space this could even be more viable since the ejecta from the ablative heat shield will just stay with a body in free fall and further scatter incoming radiation at least a little.

I rather thought about shorter engagements where a missile only takes tens of seconds and needs to be destroyed quickly. Each second an ablative shield buys improves the chances of a hit.