Why didn't M&S sue other stores for "copycat" caterpillar cakes?

[Star555]

www.bbc.com/news/business-56756731

M&S now suing Aldi for "Cuthbert the Caterpillar"...but why didn't they sue other stores for the their Colin the Caterpillar imitation cakes like Tesco's Curly or Sainsbury's Wiggles?

UPDATE: The Colin vs Cuthbert war is now over, and it looks like Colin came out on top!
www.theguardian.com/business/2022/feb/01/marks-spencer-and-aldi-call-truce-in-colin-the-caterpillar-cake-war

"Details of the deal, which was finalised in the high court last week, have not been revealed, but it is understood that Cuthbert will not appear again in quite the same form."

Imagine studying for years to be a lawyer, only to be assigned to a case defending copyright on a caterpillar-shaped cake