Why do some British people stop saying "thank you"?

Millions of Brits have ditched the traditional "thank you" and replaced it with the less formal "cheers" , according to a poll.(11)Although the average person will say "thank you" nearly 5 ,000 times a year, one in three are more likely to throw in a "cheers" or "ta" where it’s needed, rather than risk sounding old fashioned. One in 20 now say "nice one" instead, while younger generations are more likely to offer a" cool "than a" thank you".
    One in twenty who took part in the poll of 2,000 people by the Food Network UK for Thank You Day, which is marked on November 24 said a formal "thank you" was now not often needed in everyday conversation.(13)More than one in ten adults said they regularly won’t say "thank you" if they are in a bad mood. Most people claimed that saying "thank you" was something drilled into them by their parents, but four in ten will utter a "thank you" purely out of habit.(14)A huge 70 percent of those questioned will say "thank you" to a person’s face without even meaning it, while a fifth avoid saying it when they know they should—on at least two occasions every day.