I think its funny that those two names are popular baby names recently.
I don’t know anyone with a child named Max. Years ago, I knew one family with a “Maximilian,” named for St. Maximilian Kolbe.
I know two or three families with a “Maribel” or “Isabel” who is called “Bella” or “Belle.”
Don’t know anyone with these pet names, either. We have to remember that this is one Boston vet’s experience, not a statistically-valid nationwide survey.