In the age of streaming, dubbing a US cartoon into UK English seems wasteful. But in 2005, the market was different.
British broadcasters (specifically Nick Jr. UK and Channel 5's Milkshake! ) had a rule: Research at the time suggested that very young children (ages 2-4) struggled to parse the rhotic, hard "R" sounds of General American English. A character saying "sup-er" vs "supp-ah" could cause cognitive friction. backyardigans uk dub