that's the whole point really, when it comes down to it, if the meerkat is a pet (as the thread title says) and it is kept singly then the owner needs to spend as much time as possible with it to give it an acceptable life, just as with the examples of dog or parrot. Unfortunately, owners rarely do, and the dog is restricted to a kennel all day alone and the parrot is stuck in a little cage all day alone.
Ideally meerkats being kept privately should be in social groups so thye can keep each other occupied, but in that case they're not really pets any more than the ones in zoos are.
I do always find it interesting that people get so het up about "wild" animals being kept as "pets" (ie by private owners) but not a word is spoken about the atrocious conditions that many other species such as rabbits or hamsters are kept in. Relatively few "wild" animals are kept privately and many of those keepers are very dedicated, often providing better conditions than in the zoos.