Post-World War I, milk bottles were sealed with aluminum foil caps. By the 1950s, the entire population of blue tits in the UK had learned to open these caps to reach the cream left by the milkman.
Many Britons had to leave special plastic caps on their doorsteps to protect the bottles from tit raids, as the birds even learned the milkman's delivery schedule.
Blue tits learned this, while robins did not. It all comes down to their ability to pass on accumulated knowledge. Blue tits live in flocks, and young birds learn from experienced individuals. New behavior spread from a few birds to hundreds in a matter of weeks. Robins, on the other hand, are solitary, and even if one bird learns to open a cap, it can't pass on its knowledge.