Why do British people say thank you so much?

Excuse me, but could you elaborate on why British individuals tend to express their gratitude so frequently with the phrase "thank you so much"? Is this a cultural norm rooted in politeness or perhaps a reflection of their upbringing and social etiquette? Is there a historical context or societal pressure that encourages such a profound display of appreciation? I'm genuinely curious about the underlying reasons behind this common practice among the British populace.