Look, anyone who chooses to have a dog as their only friend rather than be fake with people they don't even like has my respect. The Grinch might not express his love for his dog, Max, in the most effective way, but he still confides in him. We've all sat on our beds and had therapy sessions with our pets, ranting about all of our quandaries and blathering random philosophical thoughts that enter our stream of consciousness.
Sure, pets don't really understand a single word that we're saying, but they're still great listeners (actually, that quality probably makes them the best listeners). Would a human have allowed the Grinch to dress them up as Rudolph and sat quietly while he shouted about the over-commercialization of Christmas? Probably not. Max is a doggone (I'm so sorry) good friend, and it's no wonder the Grinch preferred to be with him over the Whos.