So, I understand the drawback of breaking up an object because now you have lots of objects to deal with. But wouldn’t lots of smaller objects be more likely to burn up in the atmosphere rather than one large object? Think of tossing a one ounce cube of oak into a fireplace vs one ounce of oak sawdust.
The thing to keep in mind is, even a nuke would only provide enough energy to blow a crater out of one side and bump the entire rock (and there's only one or perhaps a handful of bigger ones *known* that are at all a possible threat, for now) and that's the method they used here. And this particular rock isn't anywhere near being a threat, before or after this DART mission. :^)
Remember when they blew up the Death Star? The Ewoks are all burnt up and dead. Every one of them.
They were annoying in truth.