Why do companies give products different names in different countries then change the name to match

They are actually somewhat different. But unless they are tasted side by side the difference is too small to notice. For years, the company has wanted to rename the Bestfoods to Hellmann’s, but there was too much west coast resistance. Maybe they are starting the co-brand step of changing the name. I haven’t been following along.

Yes, I did work for the company for 12 years.

OK, I’m confused now too, because in AUS we have both Mars Bars and Milky Ways too.

Besides being a one-time cost, it was probably advertising money they were going to spend anyway. Snickers ads are pretty common even when they’re not changing the name (at least they are over here in the US).